ModifierShortcutTest improvement

 - After each assertion of shortcut role/category, reset invocation
   count rather than the whole mock (which clears all the stubbing).
   This is needed for an upcoming change where we will need to keep stubs
   intact during test cases
 - Correct ordering for expected, actual in assertion

Flag: TEST_ONLY
Bug: 351963350
Test: atest ModifierShortcutTests
Change-Id: Ib99310a4a310ae40a6eea4c6089e172aeb8f1cbb