FR: remove sidebar children and width restrictions

[ericlindley-g]

Context:
amp-sidebar currently disallows a broad set of children, including amp-iframe, and enforces a max-width relative to the viewport width

Initially these restrictions were in place to discourage bad UX: i.e. blocking ads, getting trapped in the sidebar with no close affordance, etc

However, the risk of supporting these experiences through sidebar is low, given the restriction that the sidebar can't be open on page load, and given that amp-bind, amp-selector, and the universal "show" action all support the same UX (albeit with slightly higher friction to do).

I propose we lift both the content and width restrictions entirely. Will bring to design review to discuss.

[aghassemi]

Related #6452

[ericlindley-g]

Notes from design review: sounds good!
Also remove !important for background scrim, and make sure that having two sidebars is OK

(also want to review sidebar 1.0 details and other options with @dvoytenko and @pbakaus)
/cc @camelburrito @torch2424

[ampprojectbot]

This issue hasn't been updated in awhile. @ericlindley-g Do you have any updates?

[ericlindley-g]

Done:
√ 2 sidebars on a page
√ broader set of children allowed

/to @camelburrito

Double-checking: are the following two also done?

• Removing max-width 80vw restriction
• Allow removing background scrim

[camelburrito]

no :(

[ampprojectbot]

This issue hasn't been updated in awhile. @camelburrito Do you have any updates?

[ampprojectbot]

This issue hasn't been updated in awhile. @aghassemi Do you have any updates?