Fix documentation for `forEachLambdaCapture` and `hasAnyCapture`

Updates the return types of these matchers' definitions to use
`internal::Matcher<LambdaCapture>` instead of `LambdaCaptureMatcher`. This
ensures that they are categorized as traversal matchers, instead of narrowing
matchers.

Reviewed By: ymandel, tdl-g, aaron.ballman

Differential Revision: https://reviews.llvm.org/D114809