Cleanups related to SkFixed.

Cleanups related to SkFixed.

This CL relands https://codereview.chromium.org/1683743005/ with two fixes:
  - Removing the test for vertical text. Vertical text doesn't work on Windows and breakText isn't supported for non-trivial text.
  - Omit PaintBreakTextTest in Google3 because we don't have the correct font setup yet.

Remove SK_FixedNaN. It does not seem to be supported or used anywhere in Skia, Chromium, Android, or Google3, (except accidentally by TwoPtRadial::kDontDrawT). I think supporting it would erase any benefit of SkFixed over float.

Remove SkBitmapFilter::lookup. It does not appear to be used anywhere in Skia, Chromium, Android, or Google3.

Fix a bug in SkPaint::breakText that limited it to ~5kB of text. Now it can handle more than 1GB.

BUG=skia:4632
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1683743005

Committed: https://skia.googlesource.com/skia/+/7ea5cb18389db11a94175de95c9db2b44972630c

patch from issue 1683743005 at patchset 120001 (http://crrev.com/1683743005#ps120001)

Review URL: https://codereview.chromium.org/1739453002