Update to Symfony 7.4.0-BETA2

This is where we run into #3522497: Passing an $options array to constraint constructors is deprecated, use named arguments instead, plus we can't call $request->get() directly any more, we have to specifically know whether we want POST (request) or GET (query) data; but in Drupal we sometimes use both interchangeable...

Finding it impossible to debug most of the remaining failures due to way too many deprecations via #3522497: Passing an $options array to constraint constructors is deprecated, use named arguments instead

Trying an upgrade of everything except symfony/validator, which hopefully we can deal with in a followup given there are many new deprecations.

Found a regression in Symfony: https://github.com/symfony/symfony/issues/62226

There are a bunch of functional test failures that I can't reproduce locally, and some Ajax JavaScript failures that I haven't had chance to investigate yet.

Some fun here in that DomCrawler now behaves differently on PHP 8.3 and 8.4 - on 8.4, Symfony now uses the native HTML5 parser instead of masterminds/html5 - so we need to make sure we run tests on both.

See https://github.com/symfony/symfony/commit/bd7fb5178b998e4f863d388850e93b...

I think this is the cause of some/most of the remaining test failures.

I think this is a second regression in Symfony: https://github.com/symfony/symfony/issues/62233

The second regression is fixed in Symfony 7.4.x-dev, but I found a third: https://github.com/symfony/symfony/issues/62236

Trying to make the MR as minimal as possible, we will have to deal with new deprecations in followups (but ideally the big ones need to be removed before 11.3.0 so contrib gets notified of them)

Currently has the following changes:

• Symfony 7.4.0-BETA1 (except symfony/validator, which has even more deprecations)
• Four new deprecation skips, which will each need a followup to solve
• Change of the DomCrawler used by BrowserTestBase to use the non-HTML5 parser in PHP 8.4 (there are some incompatibilities that I have opened Symfony issues for)
• Change of the default Content-Type header charset from "UTF-8" to "utf-8" (affects many tests)

First green run. Let's try adding back symfony/validator...

This is now the minimal amount of changes required to land 7.4.0-BETA1, all deprecation skips or other temporary fixes (such as the "UTF-8" to "utf-8" change) have been moved to child issues of #3555526: Update to Symfony 7.4.0.

We will have to figure out how to solve the ampersand issue over in #3555527: Since symfony/dom-crawler 7.4: Disabling HTML5 parsing is deprecated. Symfony 8 will unconditionally use the native HTML5 parser. The code generates some very questionable HTML for the sake of an XSS-like test but I'm not sure how valid it really is. https://github.com/symfony/symfony/pull/62252 has comments from both a Symfony maintainer and the author of the PHP HTML5 extension commenting that my solution was a bad idea, so I will go along with what they say!

Bumped to BETA2: https://symfony.com/blog/symfony-7-4-0-beta2-released

This means we can remove a workaround for a bug in beta1 that was fixed in beta2: https://github.com/symfony/symfony/issues/62226

@andypost Followups for the deprecations all exist as children of #3555526: Update to Symfony 7.4.0

Not sure we need a change record, we haven't made any API changes - this is just a release notes thing really. We might need change records for some of the deprecations but that will happen in the followups.