web: Throw an error when reference types are unsupported

[danielhjacobs]

This is somewhat the antithesis of #18528. That PR keeps Ruffle running on browsers without reference types support. This instead forces an error on those browsers.

Merging #18399 will break Ruffle on Safari versions below 15 and Pale Moon. We can keep Ruffle working on those browsers, or we can officially designate them to be unsupported.

[danielhjacobs]

Note: Right here, it would be possible by exporting isFlashEnabledBrowser from the polyfills file and importing it here to add this code:

                if ("url" in options && isFlashEnabledBrowser()) {
                    const flashEmbed = Object.assign(document.createElement('embed'), {
                        src: new URL(options.url, document.baseURI).href,
                        width: "100%",
                        height: "100%",
                    });
                    this.container.textContent = "";
                    this.container.appendChild(flashEmbed);
                    return;
                }

That would create a Flash embed on Flash-enabled browsers which do not have reference-types support when using the Ruffle API with a URL (rather than a data buffer). It ignores any configuration options in favor of simplicity, though we can be less simple by doing this: https://github.com/ruffle-rs/ruffle/pull/16523/files#diff-467a580c71d4e3b96032b54a2a292d485f3b83f87ba2478daf693bac6d532965R1019-R1041

That said, it may not be desired as noted in #16523

[danielhjacobs]

danielhjacobs/ruffle@throw-direct-error-when-reference-types-unsupported...danielhjacobs:ruffle:make-embed-if-flash-supported-ruffle-not

This would create Flash embeds if reference-types is unsupported but Flash is supported. I mainly just wrote it for fun, as it was interesting to try to let DataLoadOptions work too.