internal/coverage: refactor EmitTextual in preparation for bugfix
Refactor cformat.EmitTextual to accept a package filter (list of
packages to report). This is a no-op in terms of exposed coverage
functionality, but we will need this feature in a subsequent patch.
Updates #70244.
Change-Id: I1e6bcbfb5e68187d4d69d54b667e97bc1fdfa2d4
Reviewed-on: https://go-review.googlesource.com/c/go/+/627315 Reviewed-by: David Chase <drchase@google.com> Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>