RFR: 8260245: Update ICU4C to version 68.2

[Kevin Rushforth]

On Mon, 5 Apr 2021 18:14:36 GMT, Arun Joseph <ajoseph at openjdk.org> wrote:

> We currently use ICU4C version 64.2. We should update to the latest stable version 68.2.
> http://site.icu-project.org/home

Overall this looks good. I'll review / test it in detail later.

Quick comments on the PR:

1. You need to update the version number in `.../legal/icu_web.md`
2. Related to the above, can you create a new `UPDATING.txt` file in `.../native/Source/ThirdParty/icu` with instructions as to what needs to be updated when updating to a new ICU version, specifically including the changes to `build.gradle`, `.../legal/icu_web.md`, and `/native/Source/ThirdParty/icu/CMakeLists.txt` regarding updating the version number, along with anything else that isn't obvious (although I think the rest is straight-forward)?
3. Will the changes in core WebKit code (e.g., `TRUE` --> `true`) cause merge conflicts in the future?

Also, since this also addresses [JDK-8232379](https://bugs.openjdk.java.net/browse/JDK-8232379), can you add it to this PR with `/issue add 8232379`?

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PR: https://git.openjdk.java.net/jfx/pull/456