79959 Unblock roll by reverting #79061 (a: tests, team, framework, cla: yes)

79961 Mark integration_test_test as unflaky (team, cla: yes, team: flakes, waiting for tree to go green)

79975 Use testUsingContext in downgrade_upgrade_integration_test (a: tests, team, tool, cla: yes, waiting for tree to go green)

79985 Convert some general.shard base tests to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

80002 Migrate more tool unit tests to null safety (team, tool, cla: yes, waiting for tree to go green, a: null-safety)

80003 Refactor text editing test APIs (Mark III) (a: tests, team, framework, cla: yes, waiting for tree to go green)