🐛 Replace internal version with compile time constant (ampproject#21832)

* Replace internal version with compile time constant

This implements a compile time constant replacement for the AMP Version magic string. This also fixes the last remaining issue with sourcemaps, caused by the old string replace not keeping the same number of chars in the replacement.

```js
// input
import {version} from './internal-version';
version();

// output
"1904010000000"
```

* Clean up nit

Revert "🏗 Replace `gulp-closure-compiler` with `google-closure-compil…

…er` (ampproject#21868)" (ampproject#21879)

This reverts commit 606c597.

Reason for revert: `gulp dist` is really slow with `google-closure-compiler`.

amp-bind: Wait for init before scanAndApply (ampproject#21763)

* Wait for bind.init before scanAndApply.

* Add todo.

✨amp-experiment-v1: Created experiment for amp-experiment-v1 (ampproj…

…ect#21663)

* Added support for the experiment

* Precommit, and test to check experiment

* nit: extra newline

* Fixed dep check

Revert "🐛Change check to see if amp-img has completed layout. (amppro…

…ject#21483)" (ampproject#21613)

This reverts commit a628902.

🐛Find media inside FIE (ampproject#21579)

🐛Find media inside FIE (ampproject#21579)

📦 Update dependency sinon to v7.2.7 (ampproject#21216)

🐛 Fix bad translate from refactor (ampproject#21336)

Mea culpa. Fixes ampproject#21332 introduced by ampproject#20905.

Will introduce tests in a later PR so this won't happen again.

🐛 Fix bad translate from refactor (ampproject#21336)

Mea culpa. Fixes ampproject#21332 introduced by ampproject#20905.

Will introduce tests in a later PR so this won't happen again.