[skunicode] Consolidate SkUnicode_IcuBidi

Move all of SkUnicode_IcuBidi into skunicode_icu_bidi.cpp. This removes
duplicate definitions and allows building any combination of SkUnicode
implementations.

Change-Id: Iaca4187b8f76107492bffbc073dd84004bec0753
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/740716
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
7 files changed