In the UTF-8 implementation, this prevents out-of-bounds access of the
underlying text data, as the ICU macro would essentially do something
akin to `text[text.length()]`.
The UTF-16 implementation already checks for out-of-bounds, but would
previously return 0. We now return an empty Optional in both impls. This
doesn't affect LibJS (the user of the UTF-16 impl), as it already does
bounds checking before invoking LibUnicode APIs.
C++ will jovially select the implicit conversion operator, even if it's
complete bogus, such as for unknown-size types or non-destructible
types. Therefore, all such conversions (which incur a copy) must
(unfortunately) be explicit so that non-copyable types continue to work.
NOTE: We make an exception for trivially copyable types, since they
are, well, trivially copyable.
Co-authored-by: kleines Filmröllchen <filmroellchen@serenityos.org>
The gist is that we need to construct an ICU date-time formatter for
each possible Temporal type. This is of course going to be expensive.
So instead, we construct the configurations needed for the ICU objects
in the Intl.DateTimeFormat constructor, and defer creating the actual
ICU objects until they are needed.
Each formatting prototype can also now accept either a number (as they
already did), or any of the supported Temporal objects. These types may
not be mixed, and their properties (namely, their calendar) must align
with the Intl.DateTimeFormat object.
