Fixed Literal String intern mismatch.

Literal Strings in app images are interned into local intern tables
which causes mismatch with the runtime intern table, especially when
a string is loaded from app images twice. Now when .art is loaded, a
visitor go through all classes and their fields to intern every string
literal found again.

Test case 596 is updated to test the string intern functioanlity.

Test on devices Nexus 5X, fixing strings takes 5.4 ms on GoogleMap
during startup.

Bug: 62224799

Test: test-art-host -j64

Change-Id: I2e1d44a79db1ae5f9aec80f228128201d1d838d8