Support text transformations in icu::message2

[grhoten]

The following text transformations that are available in Unicode Inflection should be hooked into icu::message2.

• upper case: HELLO WORLD
  • StringViewUtils::uppercase or call ICU.
• lower case: hello world
  • StringViewUtils::lowercase or call ICU.
• title case: Hello World
  • Call ICU.
• sentence case: Hello world
  • StringViewUtils::capitalizeFirst
• quote: "Hello world"
  • CommonConceptFactory::quote
  • It's not clear if quoted patterns does the same thing. See QuoteTest.cpp for the context sensitive quoting that it performed that is not supported by ICU nor CLDR by default.

Ideally, these text transformations should be chainable. So I could apply sentence casing and then quote it.