[clang-tools-extra] [clangd] forward clang-tidy's readability-identifier-naming fix to textDocument/rename (PR #78454)

[Tom Praschan via cfe-commits]

tom-anders wrote:

> Something else I noticed while trying out the patch locally: before the patch, the description of the code action in the editor is "change 'foo' to 'Foo'", i.e. a description of what the code action will do.
> 
> After the patch, the description of the code action is now "invalid case style for function 'foo'", i.e. it describes the problem, not the fix.
> 
> We should keep the description of the code action the same, i.e. describing the fix.

Ah good find, I added a new `FixMessage` field for this (and also added this to the test)

https://github.com/llvm/llvm-project/pull/78454