[clang-tools-extra] Follow style configuration in clangd when inserting missing includes (PR #140594)

[kadir çetinkaya via cfe-commits]

================
@@ -151,6 +164,11 @@ std::vector<Diag> generateMissingIncludeDiagnostics(
     if (!Replacement.has_value())
       continue;
 
+    if (Angled && Spelling.front() == '\"') {
----------------
kadircet wrote:

yikes, we also need to do this transformation in the other way as well :/

Might be easier to:
```cpp
if (Angled != (Spelling.front() == '<')) {
  Spelling.front() = Angled ? '<' : '"';
  Spelling.back() = Angled ? '>' : '"';
}
```

(I guess we're also lacking some tests for the quoted direction)

https://github.com/llvm/llvm-project/pull/140594