[jdk18u] RFR: 8284680: sun.font.FontConfigManager.getFontConfig() leaks charset

[Zhengyu Gu]

A clean backport to fix memory leaks.

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Commit messages:
 - Backport dea6e886af20457597dd02dacf1e80273a7165a7

Changes: https://git.openjdk.java.net/jdk18u/pull/150/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=150&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8284680
  Stats: 18 lines in 1 file changed: 18 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk18u/pull/150.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18u pull/150/head:pull/150

PR: https://git.openjdk.java.net/jdk18u/pull/150