Fixes a4a should validate test failure (ampproject#5847)

Fix typo and spacing (ampproject#5739)

Allow webviews to be set as trusted viewers (ampproject#5592)

* Allow webviews to be set as trusted viewers

Webviews can't set `ancestorOrigins` properly (maybe?), we can't use it
to tell if we are in a trusted viewer context. Instead, fall back to our
"old browser" path, which creates a `trustedViewerResolver_`. When the
webview's integration script [sets the message
deliverer](https://github.com/ampproject/amphtml/blob/f28e116/src/service/viewer-impl.js#L947),
it [will
resolve](https://github.com/ampproject/amphtml/blob/f28e116/src/service/viewer-impl.js#L961-L962)
to the webview's passed origin.

Fixes ampproject#5563.

* Add tests

* Do not trust "webviews" that are really bad actor iframes

We treat them like normal iframes.

* Test for '1' explicitly

* Fix test

Implementation and documentation of AdvertServe <amp-ad> tag (ampproj…

…ect#5366)

* Implementation and documentation of AdvertServe <amp-ad> tag

* Implementation and documentation of AdvertServe <amp-ad> tag

* Removed changes that weren't needed

* Added the <fallback> tag

* Implemented renderStart

Fix PR check on new branches (ampproject#5455)

Dont make sidebar mask diaplay:none by default. (ampproject#5365)

Fixes
Can't dismiss sidebar with click on main page content ampproject#5362

Fix borders on body after lightbox mode is enabled. (ampproject#5299)

Fix amp img lightbox (ampproject#5279)

* ImageViewer class does not inherit `loadPromise`

* add simple test

* bind the function passed in since it is an instance method

don't remove side effect dist --fortesting (treated as dev) (ampproje…

…ct#5202)

Snap to the correct slide on orientationChange. (ampproject#5120)

* Snap to the correct slide on orientationChange.

* Add tests