Fix contentcapture perf tests not executed

When start running tests, the test tool will search all large test cases.
But the tool cann't find @LargeTest from class parent. Moves @LargeTest to
sub-class.

Bug: 153770130
Test: adb shell am instrument -w -r --no-hidden-api-checks -e debug false \
 -e newRunListenerMode true -e size large -e log true -e timeout_msec 240000 \
 com.android.perftests.contentcapture/androidx.test.runner.AndroidJUnitRunner
Change-Id: I1a276077e754f348cf814c3a3aeb7ee32c48bdda