RFR: 8218640: Update ICU4C to version 64.2

[Arun Joseph]

We currently use ICU4C version 62.1. We should update to the latest stable version 64.2.
http://site.icu-project.org/home

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Commits:
 - b56b720e: 8218640: Update ICU4C to version 64.2

Changes: https://git.openjdk.java.net/jfx/pull/10/files
 Webrev: https://webrevs.openjdk.java.net/jfx/10/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8218640
  Stats: 41065 lines in 430 files changed: 23684 ins; 7205 del; 10176 mod
  Patch: https://git.openjdk.java.net/jfx/pull/10.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/10/head:pull/10

PR: https://git.openjdk.java.net/jfx/pull/10