77983 Remove MockBuildSystem from generate_synthetic_packages_test (cla: yes, team, tool, waiting for tree to go green)

77985 MockProcessUtils->FakeProcessManager in version_test (cla: yes, team, tool, waiting for tree to go green)

77986 Remove mocks from build_windows_test (cla: yes, team, tool, waiting for tree to go green)

77988 MockOperatingSystemUtils -> FakeOperatingSystemUtils (cla: yes, team, tool, waiting for tree to go green)

77991 Remove mock from cocoapods_validator_test (cla: yes, team, tool)

78078 Enable subshard builders for pre-submit (cla: yes, team, waiting for tree to go green)

78089 Remove MockFlutterVersion from mocks (cla: yes, team, tool)