Implement AMP_STATE() URL variable that reads from the amp-bind state

[josh313]

• Implements the second action item from amp-analytics: Shared interpolation & ampState() URL variable #13079

@choumx

[dreamofabear]

Thanks for working on this.

Perhaps we should limit these expressions to only object dereferences, e.g. x.y.z not random(). We have a function helper for this in json.js#getValueForExpr(), which is also nice since we won't need to have a web worker roundtrip.

[josh313]

@choumx I updated it to use the getValueForExpr now. Thanks for the suggestion.

I'm getting a bundle size error now. What should I do about that?

[dreamofabear]

Probably due to the new code in url-replacements-impl. I helped bump the size cap, should be good now.