Update ICU plural examples in JSON formats

[dbendilas]

Problem and/or solution

Update KEYVALUEJSON and STRUCTUREDJSON examples of pluralized
ICU strings, so that the starting keyword is the same as the
variable name.

For example {count, plural, one {{cnt} item} other {{cnt} items}}
is best written as {cnt, plural, one {{cnt} item} other {{cnt} items}}.
The reason is that many ICU libraries or frameworks will probably
require the two to be identical (cnt), not count for the keyword
and cnt for the variable placeholder.

How to test

Not much to test, it's a documentation change, really. The unit tests should pass, of course.

Reviewer checklist

Code:

• Change is covered by unit-tests
• Code is well documented, well styled and is following best practices
• Performance issues have been taken under consideration
• Errors and other edge-cases are handled properly

PR:

• Problem and/or solution are well-explained
• Commits have been squashed so that each one has a clear purpose
• Commits have a proper commit message according to TEM