Fix Custom Element instance creation in IE11 (#25245)
Fix Custom Element instance creation in IE11 (#25245)

When we transpile `super` in Custom Element subclasses, we change it to
`superClass.call(this)` (where `superClass` is `HTMLElementPolyfill`).
That `.call` value is inherited from `Function.prototype`.  But, IE11's
native HTMLElement hierarchy doesn't extend from Function!  And because
`HTMLElementPolyfill` extends from `HTMLElement`, it doesn't have a
`.call`! So we need to manually install it.
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