Previously, when an input property was initially set to `undefined` it
would not be correctly recognized as a change (and trigger
`ngOnChanges()`).
This commit ensures that explicitly setting an input to `undefined` is
correctly handled the same as setting the property to any other value.
This aligns the behavior of Angular custom elements with that of the
corresponding components when used directly (not as custom elements).
PR Close#36140
Previously, when an input property was set on an `NgElement` before
instantiating the underlying component, the `SimpleChange` object passed
to `ngOnChanges()` would have `firstChange` set to false, even if this
was the first change (as far as the component instance was concerned).
This commit fixes this by ensuring `SimpleChange#firstChange` is set to
true on first change, regardless if the property was set before or after
instantiating the component. This alignthe behavior of Angular custom
elements with that of the corresponding components when used directly
(not as custom elements).
Jira issue: [FW-2007](https://angular-team.atlassian.net/browse/FW-2007)
Fixes#36130
PR Close#36140
