Increase coverage for the Intl.DateTimeFormat constructor by adding a
test that confirms that ToObject(...) is appropriately called inside the
implementation.

Increase coverage for the Intl.DateTimeFormat constructor by adding a
test that checks for the default values.

Four tests were documented as asserting the interpretation of line
terminators within multi-line comments, but the source code did not
actually demonstrate this condition.

Introduce new tests that demonstrate the intended functionality and
place them in the correct directory.

Previously, these tests simply compared against an equivalent regular expression pattern by generating a large string containing either all code points up to U+FFFF or U+10FFFF, depending on the `u` flag, and then performing:

    str.replace(re, '') === str.replace(otherRe, '');

These two `String#replace` calls can be optimized into a single `RegExp#test` call by following the pattern used in the property escapes tests at https://github.com/mathiasbynens/unicode-property-escapes-tests.

RegExp.prototype is not a RegExp, and the algorithm only special-cases
(same-realm) %RegExpPrototype%.

Based on: https://github.com/tc39/test262/blob/44fc8165d54de9c9f0128f70eda56bdcb5dde82c/implementation-contributed/v8/intl/segmenter/segment-iterator-ownPropertyDescriptor.js

Fix wrong expectations of
Intl.RelativeTimeFormat.prototype.formatToParts
Add tests to cover "group", "decimal" and "fraction".

Fixes #1904