go/parser: add data-driven tests for object resolution

Add new tests for object resolution driven by source files with
declarations and uses marked via special comments. This made it easier
to add test coverage while refactoring object resolution for #45104.

Tests are added to a new resolver_test.go file. In a subsequent CL the
resolver.go file will be added, making this choice of file name more
sensible.

For #45104
For #45136
For #45160

Change-Id: I240fccc0de95aa8f2d03e39c77146d4c61f1ef9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/304450


Trust: Robert Findley <rfindley@google.com>
Trust: Robert Griesemer <gri@golang.org>
Run-TryBot: Robert Findley <rfindley@google.com>
Reviewed-by: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>