go/types,types2: avoid data race to object.color_ through dot imports
As described in issue #69912, type checking dot-imported identifiers can
result in a call to objDecl on an imported object, which leads to a data
race to the color_ field.
There are multiple potential fixes for this race. Opt for avoiding the
call to objDecl altogether, rather than setting color_ during import.
The color_ field is an internal property of objects that should only be
valid during the type checking of their package. We should not be
calling objDecl on imported objects.
Fixes #69912
Change-Id: I55eb652479715f2a7ac84104db2f448091c4e7ac
Reviewed-on: https://go-review.googlesource.com/c/go/+/621637
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Auto-Submit: Robert Findley <rfindley@google.com> Reviewed-by: Alan Donovan <adonovan@google.com>