[clang-tools-extra] [clangd] Implement simple folding of preprocessor branches (PR #80592)

[Ruihua Dong via cfe-commits]

144026 wrote:

Any updates on pseudo parser removal? It seems like clangd/vscode-clangd#297 is open for this as well, and people have been using vscode-explicit-folding as a workaround.
@sam-mccall Would it be possible to apply and keep pp folding support before foldingRange support is put back on AST parser?

https://github.com/llvm/llvm-project/pull/80592