feat: Add break <line-number> command

This makes it much easier to find the correct place to add a break point
while debugging a program.

For example, now one can do the following:

```
$ cd test_programs/execution_success/merkle_insert/
$ nargo debug
[merkle_insert] Starting debugger
At opcode 0: BRILLIG CALL func 0: PREDICATE = %EXPR [ 1 ]%
inputs: [Single(Expression { mul_terms: [], linear_combina [...]
> next
At opcode 0.17: Const { destination: MemoryAddress(21), bi [...]
At [...]/test_programs/execution_success/merkle_insert/src/main.nr:12:3
  7    ...
  8        new_root: pub Field,
  9        leaf: Field,
 10        index: Field,
 11        mimc_input: [Field; 4]
 12 -> ) {
 13        assert(old_root == std::merkle::compute_merkle_ [...]
 14
 15        let calculated_root = std::merkle::compute_merk [...]
 16        assert(new_root == calculated_root);
 17
 18        let h = mimc::mimc_bn254(mimc_input);
 19        // Regression test for PR noir-lang#891
 20        std::println(h);
 21        assert(h == 18226366069841799622585958305961373 [...]
 22    }
> break 18
Added breakpoint at opcode 0.1274
> continue
(Continuing execution...)
Stopped at breakpoint in opcode 0.1274
At opcode 0.1274: Const { destination: MemoryAddress(36),  [...]
At /home/stan/code/repos/noir/test_programs/execution_succ [...]
 13    ...
 14
 15        let calculated_root = std::merkle::compute_merk [...]
 16        assert(new_root == calculated_root);
 17
 18 ->     let h = mimc::mimc_bn254(mimc_input);
 19        // Regression test for PR noir-lang#891
 20        std::println(h);
 21        assert(h == 18226366069841799622585958305961373 [...]
 22    }
>
```

tooling/debugger/src/context.rs

@@ -178,6 +178,17 @@ impl<'a, B: BlackBoxFunctionSolver<FieldElement>> DebugContext<'a, B> {
             .filter(|v: &Vec<Location>| !v.is_empty())
     }
 
+    /// Returns the `FileId` of the file associated with the innermost function on the call stack.
+    pub(super) fn get_current_file(&mut self) -> Option<FileId> {
+        match self.get_current_source_location() {
+            Some(locations) => match locations.last() {
+                Some(location) => Some(location.file),
+                None => None,
+            },
+            None => None,
+        }
+    }
+
     /// Returns the (possible) stack of source locations corresponding to the
     /// given opcode location. Due to compiler inlining it's possible for this
     /// function to return multiple source locations. An empty vector means that

tooling/debugger/src/repl.rs

@@ -199,6 +199,70 @@ impl<'a, B: BlackBoxFunctionSolver<FieldElement>> ReplDebugger<'a, B> {
         }
     }
 
+    fn add_breakpoint_at_line(&mut self, mut line_number: usize) {
+        // Make line number 0-indexed.
+        line_number -= 1;
+
+        let current_file = match self.context.get_current_file() {
+            Some(file) => file.clone(),
+            None => {
+                println!("No current file.");
+                return;
+            }
+        };
+
+        let mut best_start: usize = 0;
+        let mut best_location: Option<OpcodeLocation> = None;
+
+        // Helper function that first finds the source locations associated with the given opcode.
+        // Then, it finds the start and end lines of the source location and
+        // updates the best_start and best_location temporaries, if the given opcode_location
+        // matches the desired break-line better than the previous best match.
+        let mut update_best_match = |opcode_location: OpcodeLocation| {
+            let source_locations =
+                self.context.get_source_location_for_opcode_location(&opcode_location);
+            // Last means inner-most in stack trace.
+            match source_locations.last() {
+                Some(source_location) => {
+                    let start = self.debug_artifact.location_line_index(*source_location).unwrap();
+                    let end =
+                        self.debug_artifact.location_end_line_index(*source_location).unwrap();
+                    if source_location.file == current_file
+                        && start <= line_number
+                        && line_number <= end
+                        && line_number - start < line_number - best_start
+                    {
+                        best_start = start;
+                        best_location = Some(opcode_location);
+                    }
+                }
+                None => (),
+            }
+        };
+
+        let opcodes = self.context.get_opcodes();
+        for (acir_index, opcode) in opcodes.iter().enumerate() {
+            match &opcode {
+                Opcode::BrilligCall { id, .. } => {
+                    let bytecode = &self.unconstrained_functions[*id as usize].bytecode;
+                    for (brillig_index, ..) in bytecode.iter().enumerate() {
+                        let opcode_location = OpcodeLocation::Brillig { acir_index, brillig_index };
+                        update_best_match(opcode_location);
+                    }
+                }
+                _ => {
+                    println!("Not supported: break-line for {:?}", opcode);
+                    return;
+                }
+            }
+        }
+
+        match best_location {
+            Some(location) => self.add_breakpoint_at(location),
+            None => println!("No opcode at line {}", line_number),
+        }
+    }
+
     fn delete_breakpoint_at(&mut self, location: OpcodeLocation) {
         if self.context.delete_breakpoint(&location) {
             println!("Breakpoint at opcode {location} deleted");
@@ -475,6 +539,16 @@ pub fn run<B: BlackBoxFunctionSolver<FieldElement>>(
                 }
             },
         )
+        .add(
+            "break",
+            command! {
+                "add a breakpoint at a line of the current file",
+                (line_number: usize) => |line_number| {
+                    ref_context.borrow_mut().add_breakpoint_at_line(line_number);
+                    Ok(CommandStatus::Done)
+                }
+            },
+        )
         .add(
             "break",
             command! {