Move all usage of versioned_static to media methods

[tomkins]

To avoid staticfiles manifest file checking during loading of models, ensure that all versioned_static calls are only used inside media methods.

Change versioned_static so that the static() call is done after the test for hashed staticfiles being used.

Closes #5693.

To test:

pip install -e git+https://github.com/tomkins/wagtail.git@versioned-static#egg=wagtail
wagtail start versionedstaticdemo
cd versionedstaticdemo
echo "SECRET_KEY='secret'" > versionedstaticdemo/settings/local.py
cat > home/models.py <<EOF
from django.db import models

from wagtail.admin.edit_handlers import FieldPanel
from wagtail.core.models import Page
from wagtail.core.fields import RichTextField


class HomePage(Page):
    rich_text = RichTextField()

    content_panels = Page.content_panels + [
        FieldPanel("rich_text", classname="full"),
    ]
EOF
./manage.py makemigrations --settings=versionedstaticdemo.settings.production --dry-run --check

[squash-labs]

Manage this branch in Squash

Test this branch here: https://tomkinsversioned-static-lznic.squash.io

[frmdstryr]

Related #5644, appears that was not fully complete.

[gasman]

Thanks @tomkins!

[tomkins]

My original intention was to avoid tweaking versioned_static as that felt like the right thing, so the main focus was to get anything which used it into a media method to avoid being called too early.

However we could just change that function and leave the rest alone. It's a much smaller PR - and feels a lot less invasive.

I'm happy to bring back the original code and address some more of the original feedback if you prefer.

[tomkins]

Hopefully the third attempt should be a bit better:

• versioned_static will now immediately return the exact string back if it's an absolute URL already - which matches Django's behaviour.
• Updated DraftailRichTextArea a bit more, as plugin media can't be merged during __init__ - combining media together result in the manifest being checked.
• Added versioned_static support to draftail features.
• Added cached_property to both editors media methods.

[gasman]

All looks good to me - thanks for persevering with this, @tomkins!