[clang-tools-extra] [clangd] Add support for textDocument/rangesFormatting (LSP 3.18) (PR #80180)

[Tom Praschan via cfe-commits]

tom-anders wrote:

Adapted to spec, it's now a separate request (`textDocument/range**s**Formatting`). 

Will add some tests if this gets positive feedback

https://github.com/llvm/llvm-project/pull/80180