Make pointers to glyphs in the SkGlyphCache stable

Move the SkGlyph data from the hash map into the fAlloc, and
replace it with a SkGlyph*. This simplifies implementing bulk
operation on the SkGlyphCache because already processed glyphs ptrs
will not change location when new glyphs are added to the map.

There is a very small regression, which is more than made up for in the
next CLs.

Master:
min     median  mean    max     stddev
343µs   358µs   359µs   370µs   2%

This CL:
min     median  mean    max     stddev
348µs   364µs   362µs   373µs   2%

Change-Id: I71733285ed32fa5947b588fb6dfaa0a757707646
Reviewed-on: https://skia-review.googlesource.com/c/182560
Reviewed-by: Mike Klein <mtklein@google.com>
3 files changed