Only suggest removal of as_* and to_ conversion methods on E0308

Instead of

```
error[E0308]: mismatched types
 --> tests/ui/suggestions/only-suggest-removal-of-conversion-method-calls.rs:9:5
  |
4 | fn get_name() -> String {
  |                  ------ expected `String` because of return type
...
9 |     your_name.trim() //~ ERROR E0308
  |     ^^^^^^^^^^^^^^^^ expected `String`, found `&str`
  |
help: try removing the method call
  |
9 -     your_name.trim()
9 +     your_name
```

output

```
error[E0308]: mismatched types
  --> $DIR/only-suggest-removal-of-conversion-method-calls.rs:9:5
   |
LL | fn get_name() -> String {
   |                  ------ expected `String` because of return type
...
LL |     your_name.trim()
   |     ^^^^^^^^^^^^^^^^- help: try using a conversion method: `.to_string()`
   |     |
   |     expected `String`, found `&str`
```

Fix #114329.

Author: estebank

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -261,6 +261,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             expr.kind
             && let Some(recv_ty) = self.typeck_results.borrow().expr_ty_opt(recv_expr)
             && self.can_coerce(recv_ty, expected)
+            && let name = method.name.as_str()
+            && (name.starts_with("to_") || name.starts_with("as_") || name == "into")
         {
             let span = if let Some(recv_span) = recv_expr.span.find_ancestor_inside(expr.span) {
                 expr.span.with_lo(recv_span.hi())

tests/ui/suggestions/only-suggest-removal-of-conversion-method-calls.fixed

@@ -0,0 +1,16 @@
+// run-rustfix
+use std::io::stdin;
+
+fn get_name() -> String {
+    let mut your_name = String::new();
+    stdin()
+        .read_line(&mut your_name)
+        .expect("Failed to read the line for some reason");
+    your_name.trim().to_string() //~ ERROR E0308
+}
+
+fn main() {
+    println!("Hello, What is your name? ");
+    let your_name = get_name();
+    println!("Hello, {}", your_name)
+}

tests/ui/suggestions/only-suggest-removal-of-conversion-method-calls.rs

@@ -0,0 +1,16 @@
+// run-rustfix
+use std::io::stdin;
+
+fn get_name() -> String {
+    let mut your_name = String::new();
+    stdin()
+        .read_line(&mut your_name)
+        .expect("Failed to read the line for some reason");
+    your_name.trim() //~ ERROR E0308
+}
+
+fn main() {
+    println!("Hello, What is your name? ");
+    let your_name = get_name();
+    println!("Hello, {}", your_name)
+}

tests/ui/suggestions/only-suggest-removal-of-conversion-method-calls.stderr

@@ -0,0 +1,14 @@
+error[E0308]: mismatched types
+  --> $DIR/only-suggest-removal-of-conversion-method-calls.rs:9:5
+   |
+LL | fn get_name() -> String {
+   |                  ------ expected `String` because of return type
+...
+LL |     your_name.trim()
+   |     ^^^^^^^^^^^^^^^^- help: try using a conversion method: `.to_string()`
+   |     |
+   |     expected `String`, found `&str`
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0308`.