Fix bug #5846413 "phone" keyboard layout is broken on master

- was a subtle regression introduced when fixing bug #5753006
- as we are now using SkPaint::kGlyphID_TextEncoding (glyph encoding)
instead of SkPaint::kUTF16_TextEncoding (UTF16 encoding), we need to
force the UTF16 encoding in some cases that are NOT going thru
the TextLayoutCache / Harfbuzz shaping

- fix also breakText() the same way

- also clean some old comment

- Warning: depends also on a CL from Skia for having getBaseGlyphCount() "const"

Change-Id: I3d1fc87f070884876c679b33541f810fbfb5df3f