[clang-tools-extra] [clangd] Implement fold range for #pragma region (PR #168177)

[Haojian Wu via cfe-commits]

hokein wrote:

> hi, looks like this broke c++20 build bots, can you PTAL ? https://lab.llvm.org/buildbot/#/builders/108/builds/20160

oops, should be fixed in e442c67a2c98a3e1e3bfcf90aaa82ba70fb92760

https://github.com/llvm/llvm-project/pull/168177