[clangd] Simplify matches in FindSymbols tests

Summary:
Instead of checking symbol name and container (scope) separately, check the
qualified name instead. This is much shorter and similar to how it is done
in the SymbolCollector tests.

Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>

Reviewers: simark

Subscribers: ilya-biryukov, ioeric, MaskRay, jkorous, cfe-commits

Differential Revision: https://reviews.llvm.org/D47847

llvm-svn: 335624