[clang] [clang-tools-extra] [CodeCompletion] Consider header files without extension, if... (PR #166447)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

I think the most common extensionless path component in a directory named `include` will be another directory name. e.g., `include/bits/blah.h`. I tried getting clever with sourcegraph to see if I could find extensionless files in an include directory, but was unsuccessful. However, I did spot check about thirty projects and the most common extensionless files I found were hidden files like `.gitignore`. Do we have special handling for files that begin with `.` to exclude those?

CC @HighCommander4 @llvm-beanz as clangd maintainers for opinions

https://github.com/llvm/llvm-project/pull/166447