[pointer_interceptor] Mark PointerInterceptor as invisible

[harryterkelsen]

Marks PointerInterceptor as invisible.

After flutter/engine#30003 invisible platform views incur no performance penalty, as they no longer need an overlay.

Fixes flutter/flutter#94641

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[flutter-dashboard]

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[ditman]

LGTM!

@hterkelsen Can this land already, or do we need to wait for some specific flutter version to be published?

[stuartmorgan-g]

@hterkelsen What's the status here?

[ditman]

This and flutter/plugins#4578 are waiting for 2.10 to roll into stable.

[ditman]

Updating this PR to land it.

[ditman]

All green, let's go!