JIT: build pred lists before instrumentation

Move pred list building to just before instrumentation (and just after
importation -- we are getting very close to the front of the phase list now).

The block and edge count instrumenters were both using cheap preds to keep
track of some relocated count probes. Revise this so they can use the regular
pred lists. Also rework both approaches so their `RelocateProbes` methods are
fairly similar and perhaps could be unified one day.

Contributes to dotnet#80193.

src/coreclr/jit/compiler.cpp

@@ -4425,13 +4425,6 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
         return;
     }
 
-    // If instrumenting, add block and class probes.
-    //
-    if (compileFlags->IsSet(JitFlags::JIT_FLAG_BBINSTR))
-    {
-        DoPhase(this, PHASE_IBCINSTR, &Compiler::fgInstrumentMethod);
-    }
-
     // Compute bbNum, bbRefs and bbPreds
     //
     // This is the first time full (not cheap) preds will be computed.
@@ -4449,6 +4442,13 @@ void Compiler::compCompile(void** methodCodePtr, uint32_t* methodCodeSize, JitFl
     };
     DoPhase(this, PHASE_COMPUTE_PREDS, computePredsPhase);
 
+    // If instrumenting, add block and class probes.
+    //
+    if (compileFlags->IsSet(JitFlags::JIT_FLAG_BBINSTR))
+    {
+        DoPhase(this, PHASE_IBCINSTR, &Compiler::fgInstrumentMethod);
+    }
+
     // Expand any patchpoints
     //
     DoPhase(this, PHASE_PATCHPOINTS, &Compiler::fgTransformPatchpoints);