Unittests: fix DateFormatTest

When building with GCC 13, this test no longer builds correctly and errors out
because the overloaded `operator<<` for `BPrivate::BDate` and `BPrivate::BTime`
can not be found.

The underlying cause is that the libstdc++ depended on some template SFINAE
behavior, and that did not work because the `operator<<` should only be looked
up in the `BPrivate` namespace.

It is unclear whether the code for libstdc++ changed, or whether this never was
supposed to work. GCC bug #51577 seems to imply that GCC before version 12
errornously allowed the lookup of names in the global namespace. It could be
that we always relied on this behavior:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51577

Change-Id: Ia2f2306a2e97d5f19dc8c4df90a8491f22ef0bcd
Reviewed-on: https://review.haiku-os.org/c/haiku/+/6874
Reviewed-by: Adrien Destugues <pulkomandy@pulkomandy.tk>
Tested-by: Commit checker robot <no-reply+buildbot@haiku-os.org>

Locale: Support for Percent Formatting

Updates BNumberFormat to be able to format
percentages. Also re-introduces some unit
tests and updates the BNumberFormat ones.

This doesn't actually fix #16312 as the
defaults for percentage formatting don't seem
to track the selected language, but goes part
way there.

Related to #16312

Change-Id: Id6ddf426ce5571f4e8513c0eb1663cf42ac53cb1
Reviewed-on: https://review.haiku-os.org/c/haiku/+/3767
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>

BDateFormatTest: Add tests for day and month names for all format syles.

Signed-off-by: Jessica Hamilton <jessica.l.hamilton@gmail.com>

Fix BDateFormatTest: Consider timezone in test cases.

* Issue: A time_t value of say '12345678' results into different timestamps
in different timezones. So the expected output will not match the result of
BDateFormat::Format() if the calendar's timezone is different from the
timezone of the expected output, and the tests 'TestFormat' and
'TestCustomFormat' will fail.

* Fix: Add timezone information in the test cases and pass the timezone
while calling BDateFormat::Format() in order to set the calendar's
timezone same as that of the expected output.

Signed-off-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

B*Format: make immutable and remove locking

The language and formatting conventions can now only be set when
creating the objects. This removed the needs for locking them when
formatting to avoid some other thread changing the format while it's
being used.

Adjust tests and DeskBar TimeView to the API changes.

Add more tests for the DateTimePatternGenerator

There are unexpected results in some cases, with the clock switching to
12 hours format even though the locale is set to use 24 hours.

Add parsing support to BTimeFormat.

DateTimeFormat: handle custom 24 hours clock.

The "j" format pattern selects a 12 or 24 hours clock automatically
depending on the locale, but it doesn't work when the format is forced
in the locale preflet or through the BFormattingConventions API. So we
manually pick either K or H depending on that setting.

Add API for parsing dates.

Add an API to get month names.

Add tests for BDateTimeFormat with custom formats.

Reimplement BDateTimeFormat using ICU support

* Avoid hardcoding the format to "date, time"
* Allows using DateTimePatternGenerator to create custom formats from a
set of fields.

DateFormatTest: fix after ICU upgrade

* Timezone names have changed. Test the medium time format which doesn't
include them, as we aren't forcing a specific one.
* French date format also changed to use 4 digit year name.

Convert BTimeFormat tests to cppunit.

Add tests for BDateFormat.

B*Format: make immutable and remove locking

The language and formatting conventions can now only be set when
creating the objects. This removed the needs for locking them when
formatting to avoid some other thread changing the format while it's
being used.

Adjust tests and DeskBar TimeView to the API changes.

Add more tests for the DateTimePatternGenerator

There are unexpected results in some cases, with the clock switching to
12 hours format even though the locale is set to use 24 hours.

Add parsing support to BTimeFormat.

DateTimeFormat: handle custom 24 hours clock.

The "j" format pattern selects a 12 or 24 hours clock automatically
depending on the locale, but it doesn't work when the format is forced
in the locale preflet or through the BFormattingConventions API. So we
manually pick either K or H depending on that setting.

Add API for parsing dates.

Add an API to get month names.

Add tests for BDateTimeFormat with custom formats.

Reimplement BDateTimeFormat using ICU support

* Avoid hardcoding the format to "date, time"
* Allows using DateTimePatternGenerator to create custom formats from a
set of fields.

DateFormatTest: fix after ICU upgrade

* Timezone names have changed. Test the medium time format which doesn't
include them, as we aren't forcing a specific one.
* French date format also changed to use 4 digit year name.

Convert BTimeFormat tests to cppunit.

Add tests for BDateFormat.