Implement textDocument/switchSourceheader

When the current file is X.cc, there might be multiple X.h.
Use a heuristic to find the best X.h.

Vote for each interesting symbol's definitions (for header) or
declarations (for non-header). Select the file with the most votes.

If `file_id2cnt` is empty, use a simpler heuristic.

Adapt llvmorg-19-init-9465-g39adc8f42329: BuiltinType::ArraySection

Adapt llvm/llvm-project#74910: FileEntry::getName

Based on a patch by @zsrkmyn

Disable -include b.hh => -include b.hh.{gch,pch} transition

See https://maskray.me/blog/2023-07-16-precompiled-headers for the
behavior.

Adapt llvmorg-15-init-7692-gd79ad2f1dbc2: PPCallbacks::InclusionDirec…

…tive parameter

Fix short_name_size when getNameAsString does not return a prefix (#784)

Resolve "directory" in compile_commands.json in case CWD is not the p…

…roject root

Also delete an unneeded chdir hack.

Close #703

Adapt llvmorg-12-init-5498-g257b29715bb: add an argument to the ctor …

…of clang::driver::Driver

Add missing headers to adapt llvmorg-11-init-5501-g213aea4c583 and ll…

…vmorg-11-init-5528-gd7c5037e6b9

indexer: disable warnings and skip processed function bodies

Adapt clang rC370337: removal of createIndexingAction and WrappingIndexAction