[jfx11u] RFR: 8260245: Update ICU4C to version 68.2

[Kevin Rushforth]

Backport ICU update from jfx mainline to jfx11u. The backport was clean except for a minor diff in the surrounding context in `build.gradle`. I ran a sanity test on Windows (I'll test on other two platforms before integrating).

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Commit messages:
 - 8260245: Update ICU4C to version 68.2

Changes: https://git.openjdk.java.net/jfx11u/pull/3/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=3&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8260245
  Stats: 45773 lines in 673 files changed: 24665 ins; 8082 del; 13026 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/3.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/3/head:pull/3

PR: https://git.openjdk.java.net/jfx11u/pull/3