If U+FE0E is appended to the emoji code point, the glyph should have a
text presentation.
On the other hand, if U+FE0F is appended to the emoji code point, the
glyph should have an emoji presentation.

Bug: 11256006
Change-Id: I5187d44500b13a138e7ffbcf2c72e2da06374c8c

To optimize the font family search, mRanges is used for narrowing down
the search range. However, mRanges is constructed from format 4 or
format 12 entries. So, if the font supports a variation sequence but doesn't
support the base character of the sequence, the font may not be listed in
mRanges.

The proper way to fix this issue is using format 14 subtable information
for mRanges construction. However, this is not a trivial work since currently
we rely on HarfBuzz for variation sequence lookup and it doesn't provide any
API for retrieving coverage information.

Thus, as the quick fix, iterate all font families in font fallback chain if
the variation sequence is specified.

Change-Id: I278da84be8fb8f553590e2e42ed450b7e4a34eca

This issue was introduced by I22ce0e9eadc941f84e3a9b23462f194e51dd7180.
Need to decrement the two utf16 chars in KEYCAP handling.

To add unit tests, this CL also addresses the Bug: 24184208 by
introducing self built fonts since there is no good example in system
installed fonts.

Bug: 24184208
Change-Id: I23fa008adbaced78a3cb96442a6bc8892ab84ce8

This CL contains the following changes:
- Add a variation selector argument into getFamilyForChar to be able to
  select fonts which support variation selector.
- In case no fonts support the codepoint and variation selector pair,
  add a fallback rule which selects font family with ignoring variation
  selector.
- Change FontCollection::itemize to not change the font family
  immediately preceding a variation selector.
- Introduce unit tests for variation selectors.

With this CL, TextView can render the variation selectors correctly.

Bug: 11256006
Change-Id: I22ce0e9eadc941f84e3a9b23462f194e51dd7180

Introduced tests depend on installed font list in running device.
I verified these test passed  on Nexus 5(hammerhead), Nexus 6(shamu)
and Nexus 9(volantis).

Bug: 11256006
Bug: 17759267
Change-Id: I6f806370e17f6c6d3dad8df0cb70bb475a827873