amp-script: Size-changing DOM mutations on initial load

[dreamofabear]

Height-changing mutations can occur during worker-dom's "hydrating" phase (the first set of mutations), which can violate content jumping rules for amp-script[layout=container].

IOW, this line is wrong:

amphtml/extensions/amp-script/0.1/amp-script.js

Lines 363 to 364 in 4180199

	// Hydration is always allowed.
	phase != Phase.MUTATING ||

Instead, it should check whether the set of mutations contains DOM changes (e.g. attribute/child mutations, not addEventListener).

Thanks @morsssss for pointing this out. /cc @kristoferbaxter