Fix potential trace{Begin, End} mis-match issues in IMMS

Using try-finally block to ensure Trace.traceEnd will be invoked
in the end for following systrace events:
- IMMS.applyImeVisibility
- IMMS.hideMySoftInput
- IMMS.showMySoftInput

Fix: 270038435
Test: atest ImePerfTest, verify no "Unresolved events" after the test
Change-Id: If363e638b6906cd7997e055055d8d28306be3b31