ICU-21519 Make compact notation 'c' behave like 'e' in FixedDecimal

[echeran]

Checklist

• Required: Issue filed: https://unicode-org.atlassian.net/browse/ICU-21519
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Notice: the branch changed across the force-push!

• icu4j/main/tests/core/src/com/ibm/icu/dev/test/format/PluralRulesTest.java is different
• icu4j/main/tests/core/src/com/ibm/icu/dev/test/number/DecimalQuantityTest.java is different

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Notice: the branch changed across the force-push!

• icu4j/main/classes/core/src/com/ibm/icu/text/PluralRules.java is different
• icu4j/main/tests/core/src/com/ibm/icu/dev/test/format/PluralRulesTest.java is different

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[markusicu]

rslgtm

I know we discussed need this for CLDR 39 to include this data.

The changes look plausible. I would prefer if someone who has been in on these discussion could review the changes, but I don't want you (& CLDR) to be blocked.

[macchiati]

I think this works; it probably does a bit more work than it needs to, since I think it could have just mapped 'c' to 'e' on input, and 'e' to 'c' on output, rather than supporting both. But that can always be adjusted later, since this is not public api.
cc @sffc

[pedberg-icu]

OK to merge this so I can pick up an ICU with this fix for CLDR?

[pedberg-icu]

The appveyor failure is a segfault while compiling translit.cpp, certainly nothing to do with this change or (likely) even ICU. I am going to go ahead and merge this.