[clang] [clang-tools-extra] [clangd] Autocomplete fixes for methods (PR #165916)

[Nathan Ridge via cfe-commits]

================
@@ -1503,8 +1506,27 @@ void ResultBuilder::AddResult(Result R, DeclContext *CurContext,
         }
         OverloadSet.Add(Method, Results.size());
       }
-
-  R.FunctionCanBeCall = canFunctionBeCalled(R.getDeclaration(), BaseExprType);
+  R.DeclaringEntity = IsInDeclarationContext;
+  R.IsAddressOfOperand = IsAddressOfOperand;
+  R.FunctionCanBeCall = canFunctionBeCalled(R.getDeclaration(), BaseExprType) ||
----------------
HighCommander4 wrote:

In HighCommander4 at 27df471, I'm suggesting two changes to the computation of `FunctionCanBeCall`.

The first is to add `|| !IsAddressOfOperand`, as a way of avoiding needing to store the `IsAddressOfOperand` flag separately.

I do think that change deserves a comment such as this:

```
// If the user wrote `&` before the function name, assume the
// user is more likely to take the address of the function rather
// than call it and take the address of the result.
```

The second is to remove the `|| IsInDeclarationContext` part which does not make sense conceptually (if the user is writing a declaration, it's definitely not a call). I think the reason for this was so that clangd's getSignature doesn't chop off the parameters in declaration contexts, which I've addressed in my patch in a different way (passing `IncludeFunctionArguments = FunctionCanBeCall || DeclaringEntity` to `getSignature`).

https://github.com/llvm/llvm-project/pull/165916