[clangd] Fixes in lit tests
Summary:
Changes:
- `background-index.test` Add Windows support, don't create redundant `*-e` files on macOS
- `did-change-configuration-params.test` Replace `cat | FileCheck` with `FileCheck --input-file`
- `test-uri-windows.test` This test did not run on Windows displite `REQUIRES: windows-gnu || windows-msvc` (replacement: `UNSUPPORTED: !(windows-gnu || windows-msvc)`).
Reviewers: sammccall, kadircet
Reviewed By: kadircet
Subscribers: thakis, njames93, ormris, ilya-biryukov, MaskRay, jkorous, arphaman, kadircet, usaxena95, cfe-commits
Tags: #clang
Differential Revision: https://reviews.llvm.org/D83759