[Script] Fixed assorted string usage issues

* Case 1
  - Strings.equals("") or Strings == "" should be replaced with
    Strings.isEmpty()
  - Fixed using "'Strings.equals("")' inspection

* Case 2
  - Strings should never be compared with == unless we explicitly want to
    compare whether they are the same instance which is rarely the case
  - Objects.equals(A, B) does both null checks and equals() compare. Thus
    it is a safe replacement for our current usage
  - Fixed using "String comparision using '==' instaed of 'equals()'
    inspection in Intellij and accept automatic fixes

* Case 3
  - String + "" is useless and should be removed
  - Fixed using "Concatenation with empty string' inspection

* Case 4
 - String.toString() is redundant
 - Removed using 'Redundant 'String.toString()' inspection'

Bug: 63597465
Test: make checkbuild, no manual changes, no functional changes
Change-Id: Ib44d8b5dd53125eb21afa0e3d0ff6a728f67dbb8
13 files changed