Prototype ICU size reduction tooling

[steveisok]

Because the data file for ICU is quite large (~16MB), we need to prototype trying to reduce the size for iOS & tvOS.

Using https://github.com/unicode-org/icu/blob/master/docs/userguide/icu_data/buildtool.md and http://www.icu-project.org/docs/demo/datacustom_help.html as guides, we should determine the following:

• How much friction is involved? Can we easily integrate into our build?
• What is the smallest possible size configuration? Can we get down to 2MB?
• Are there any drawbacks / implications to using?

[ghost]

Tagging subscribers to this area: @ViktorHofer
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[ViktorHofer]

cc @safern

[filipnavara]

Is this still relevant? dotnet/icu already uses filtering and the artifacts are consumed on iOS.

[steveisok]

No, it's an old issue