Make most clangd unittests pass on Windows
The Windows triple currently turns on delayed template parsing, which
confuses several unit tests that use templates.
For now, just explicitly disable delayed template parsing. This isn't
ideal, but:
- the Windows triple will soon no longer use delayed template parsing
by default
- there's precedent for this in the clangd unit tests already
- let's get the clangd tests pass on Windows first before making
behavioral changes
Part of PR43592.
llvm-svn: 374718