Add TestContext parameter to ContentFromFileRuleForTests

The next CL will need a TestContext parameter in
ContentFromFileRuleForTests in order to retrieve the file rule contents
from the Config.  Add it and update all the tests that use it in order
to simply review of the next CL.

Bug: 306029038
Test: go test ./...
Change-Id: Ia4b4c9854017ea3472fa2f8ba42cf7f72720496e