[SurfaceFlinger] Refactor SurfaceInterceptorTest.

Previously, there are multiple places where we enable and disable
SurfaceInterceptor in one single test case, which makes the test fragile. This
patch refactors the code so that each test case will enable the
SurfaceInterceptor at the beginning, and disable the SurfaceInterceptor right
before the trace is captured.

BUG: 65297248
Test: adb shell /data/nativetest64/SurfaceFlinger_test/SurfaceFlinger_test
Change-Id: I96085a7ed2f6eff30932bf0cf13b4e4d59e914ed