change `value_is_output` implementation

[pngwn]

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Is your feature request related to a problem? Please describe.
We currently handle the value_is_output inside each component, it would be nice if we could pull this out into the app shell as with change events (#5309). The two are actually quite closely related because of the input/change distinction.

This coudl also be nice for custom components if we can figure something out.

[pngwn]

#5309 (comment)

[pngwn]

Not fixed