Intent to ship: Regular Expression Modifiers

[Daniel Minor]

As of Firefox 132, I intend to turn Regular Expression Modifiers on by default on all platforms. It has been developed behind the `javascript.options.experimental.regexp_modifiers` preference. The API shipped in Chromium 125 (https://developer.chrome.com/release-notes/125#regular_expression_modifiers, implementation in WebKit has not started (https://bugs.webkit.org/show_bug.cgi?id=275672).

Bug to turn on by default: https://bugzilla.mozilla.org/show_bug.cgi?id=1913752 is the bug to enable, and https://bugzilla.mozilla.org/show_bug.cgi?id=1899802 is the meta bug for this.

Standard: https://github.com/tc39/proposal-regexp-modifiers

Daniel