FYI: 8243160: Update AddToGlyphCache to handle LCD text rendering

[Jayathirth D V]

AddtoGlyphCache needs to handle RGB data and replace cells in glyphCacheLCD appropriately.
Change also contains little cleanup.

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Commit messages:
 - 8243160: Update AddToGlyphCache to handle LCD text rendering

Changes: https://git.openjdk.java.net/lanai/pull/30/files
 Webrev: https://webrevs.openjdk.java.net/lanai/30/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8243160
  Stats: 43 lines in 1 file changed: 27 ins; 9 del; 7 mod
  Patch: https://git.openjdk.java.net/lanai/pull/30.diff
  Fetch: git fetch https://git.openjdk.java.net/lanai pull/30/head:pull/30

PR: https://git.openjdk.java.net/lanai/pull/30