[clangd] Cleanup of readability-identifier-naming

Auto-generated patch based on clang-tidy readability-identifier-naming.
Only some manual cleanup for `extern "C"` declarations and a GTest change was required.

I'm not sure if this cleanup is actually very useful. It cleans up clang-tidy findings to the number of warnings from clang-tidy should be lower.  Since it was easy to do and required only little cleanup I thought I'd upload it for discussion.

One pattern that keeps recurring: Test **matchers** are also supposed to start with a lowercase letter as per LLVM convention. However GTest naming convention for matchers start with upper case. I would propose to keep stay consistent with the GTest convention there. However that would imply a lot of `//NOLINT` throughout these files.

To re-product this patch run:
```
run-clang-tidy -checks="-*,readability-identifier-naming" -fix -format ./clang-tools-extra/clangd
```

To convert the macro names, I was using this script with some manual cleanup afterwards:
https://gist.github.com/ChristianKuehnel/a01cc4362b07c58281554ab46235a077

Differential Revision: https://reviews.llvm.org/D115634

1 files changed, 4 insertions, 0 deletions

diff --git a/.clang-tidy b/.clang-tidy
index 879c3661b302..f3710d19f94f 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -6,6 +6,10 @@ CheckOptions:
     value:           CamelCase
   - key:             readability-identifier-naming.FunctionCase
     value:           camelBack
+  # Exclude from scanning as this is an exported symbol used for fuzzing
+  # throughout the code base.
+  - key:             readability-identifier-naming.FunctionIgnoredRegexp
+    value:           "LLVMFuzzerTestOneInput"
   - key:             readability-identifier-naming.MemberCase
     value:           CamelCase
   - key:             readability-identifier-naming.ParameterCase