RFR: 8269806: Emoji rendering on Linux [v18]

[Nikita Gubarkov]

> It was implemented in JetBrains Runtime a year ago and was ported & refactored for this PR
> It includes:
> - Bitmap glyph loading via Freetype
> - Manual scaling & transformation of bitmap glyphs with nearest-neighbor or bilinear-mipmap style algorithms depending on the text antialiasing hint
> - Storing BGRA glyphs in glyph cache & rendering them as plain images, as currently used XRender text drawing functions doesn't support colored glyphs
> - Small fixes in related code like null-checks which could cause NPE & comment typos

Nikita Gubarkov has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 26 commits:

 - Dynamic loading of ftcolor.h symbols on Linux.
 - Replace unicodeToUnits with Character.toChars in CCharToGlyphMapper
 - Add braces to ifs.
 - Make tests headful.
 - Merge branch 'master' into JDK-8269806
 - Remove ftcolor.c
 - Skip tests if required font is absent
 - Fix pointer to jlong conversion on x86
 - Merge branch 'master' into JDK-8269806
 - Merge branch 'master' into JDK-8269806
 - ... and 16 more: https://git.openjdk.org/jdk/compare/60c535de...57c0b57d

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Changes: https://git.openjdk.org/jdk/pull/4798/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=4798&range=17
  Stats: 2773 lines in 54 files changed: 2231 ins; 248 del; 294 mod
  Patch: https://git.openjdk.org/jdk/pull/4798.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/4798/head:pull/4798

PR: https://git.openjdk.org/jdk/pull/4798