GeezerVison

Fixes #29129

The issue to resolve this PR is not Backlog milestone.
Intl.getCanonicalLocales type definition should be included in #45647, but unfortunately it could not do.

Even now, the Intl.getCanonicalLocales type is not resolved.
We can check it in the playground.
https://www.typescriptlang.org/play?ssl=1&ssc=6&pln=1&pc=25#code/JIOwLgNgdA5gpmAwgQxAexASwMbIgGTVwjgGcg

about Intl.getCanonicalLocales

• MDN: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl/getCanonicalLocales
• ecma402 spec: https://tc39.es/ecma402/#sec-intl.getcanonicallocales

why do i add as es2016.intl

Intl.getCanonicalLocales is supported since 2016, so some proejcts using typescript might still use es2016.
I've added es2016.intl.d.ts for compatibility and defined in it.

Parameters and return types of Intl.getCanonicalLocales

UnicodeBCP47LocaleIdentifier is not defined at es2020.intl.d.ts. In the past, A comment of #39662 has tried to support UnicodeBCP47LocaleIdentifier by defining it in es2016.
However, if we do that, it will result in a destructive change for some users, as this comment states.

UnicodeBCP47LocaleIdentifier is currently an alias for string. So, as a compromise, the parameters and return value of Intl.getCanonicalLocales are defined as string. by that way, we can keep compatibility.