fix(default_value_accessor): support custom input elements that fire …

[tbosch]

…custom change events.

[tbosch]

@vsavkin FYI, had to roll back the change to the selector of DefaultValueAccessor as it breaks G3, added an integration test that explains why.

Essentially they have a custom input component that fires a change event which does not contain a target property. Therefore, the host listener of the DefaultValueAccessor failed.

[mary-poppins]

Merging PR #4878 on behalf of @tbosch to branch presubmit-tbosch-pr-4878.

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