Break grapheme clusters after viramas if they end a cluster

Previously, we stayed on the conservative side and disallowed any
grapheme breaks (and thus cursoring) where a virama was followed by a
letter, since we did not know if the virama would be forming a
cluster with the letter or not. This created problems with Indic
languages with infrequent conjuncts, such as Tamil.

Now we use the information in calculated advances to find if a
cluster is formed. If there is no cluster, we break the grapheme and
allow cursoring after the virama.

Test: Unit tests added to GraphemeBreakTests and MeasurementTests.
Test: Also manually tested Tamil sequences.
Bug: 35721792
Change-Id: Ib159edb94b3ad6f693f0d3dad016b332b2cef447

• include/minikin/GraphemeBreak.h[diff]
• libs/minikin/GraphemeBreak.cpp[diff]
• libs/minikin/Measurement.cpp[diff]
• tests/perftests/GraphemeBreak.cpp[diff]
• tests/unittest/Android.mk[diff]
• tests/unittest/GraphemeBreakTests.cpp[diff]
• tests/unittest/MeasurementTests.cpp[Added - diff]