This static function parses a subset of the language tags described in
BCP 47 (see https://www.rfc-editor.org/rfc/bcp/bcp47.txt).
Use the tag, as specified by this function, rather than the locale
identifiers components under MSW, where this should allow us to use even
locales that can't be described using just language-script-region.
We don't use empty wxLocaleIdent as default user locale and it doesn't
make much sense to do it, as the default locale is already accessible
via wxUILocale::GetDefault().
This function can now be implemented relatively straightforwardly
(although it does require an extra check under Mac), so add it, as it
can be generally useful and we're also going to need it for our own
tests in the upcoming commit.
This required changing CompareStrings() to be a method of wxUILocale
object, rather than just as a static function, as we must only allocate
the locale_t object once, and not during each to this function, as this
could make it unusably slow when using it as a comparison function when
sorting a large list of strings.
This is also more efficient under Mac, where we can similarly allocate
NSLocale only once and even marginally more efficient under MSW, where
we don't have to construct the locale string during each call. And,
under all platforms, it also simplifies code by separating this function
implementation from the initialization of wxUILocaleImpl.
Also document that case-insensitive comparison is not available under
Unix and adjust the tests accordingly.
Creating such objects (without using them for the UI) is supported under
all platforms, so allow doing it.
Note that this is only supported under Unix systems when locale_t and
related functionality is available, but this should be the case just
about everywhere by now.
Add a test (or, rather, replace an existing test which was disabled by
default) checking that we can now get locale information about any
locale, not necessarily the currently used one.
This is convenient, as it allows using a simple string such as "en" as
an argument to the functions taking wxLocaleIdent and rely on implicit
conversion, whereas previously explicitly writing either wxString("en")
or wxLocaleIdent("en") would be necessary.
Harmonize Mac and MSW versions by using case-sensitive comparison in
both of them by default, but allowing to use a flag to use
case-insensitive comparison instead.
