Add swapLabelAndValue() option to BooleanField

[ERuban]

Since 4.8.0, boolean fields on the detail page swap the usual label <-> value order (#5977). The reasoning is documented in the CSS: the label is usually a medium-long string and the value is always tiny.

This has been a recurring pain point: #6018 (open since 2023, priority: important, 16 comments) collects several requests and at least three different sets of user-land CSS workarounds. The thread doesn't ask to revert the default — it asks for an opt-in way to restore the regular order ("I am still for having some opt-in possibility for this swap").

This PR adds that option, following the style of the existing renderAsSwitch() / hideValueWhenTrue() options:

yield BooleanField::new('active')->swapLabelAndValue(false);

The default behavior doesn't change. The option defaults to true (current behavior). When set to false, the configurator adds a field-boolean-no-swap CSS class and the existing swap rules are scoped with :not(.field-boolean-no-swap) — so a disabled swap simply renders the field like every other field, with no counter-rules fighting specificity.

Includes tests, documentation and rebuilt assets (only the CSS bundle changed).

Closes #6018

[ERuban]

A possible follow-up, if there's interest: #6018 also asked for a way to configure this once for the whole backend ("or as an alternative add a setting in the Dashboard/Crud config classes"). This could be a Crud option set in configureCrud() (dashboard-wide or per CRUD controller), with the field-level swapLabelAndValue() overriding it - the same cascade that Crud::setThousandsSeparator() and the number fields already use.

Happy to send that as a separate PR if you think it fits - this one stays field-level only to keep it small.