internal/lsp: elide details for non-package files
internal/lsp: elide details for non-package files

When gc_details is invoked on a file, it can add diagnostics for files
not in that file's package. Some of these will not go away when
gc_details is toggled off. The fix is not emitting compiler details
diagnostics about files not in the package.

Fixes: https://github.com/golang/go/issues/42198
Fixes golang/go#42198
Change-Id: Ib69cdd8b7be96d73ee417711f7241f56fb529836
Reviewed-on: https://go-review.googlesource.com/c/tools/+/266342
Trust: Peter Weinberger <dd140fb9530d791057dd8833ea6768ff65fcde71@google.com>
Reviewed-by: Rebecca Stambler <d7cf11e5f299d88ea8348366a9fc4f7c335c3afa@golang.org>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools