Block Bindings API/UI: Don't show post meta fields that start with an underscore _

[bacoords]

What problem does this address?

It's a precedent that post meta fields starting with an underscore are "hidden" and don't show up in the regular Custom Fields UI. Feels like they shouldn't show up in the new Block Bindings UI either:

https://developer.wordpress.org/reference/functions/add_post_meta/#comment-467

What is your proposed solution?

Only show post meta fields that don't start with an underscore.

Related Conversation: #64570 (comment)

[justintadlock]

It would be correct to hide post meta with keys that begin with an underscore. These are considered "private" meta keys and should never appear in admin UIs: https://developer.wordpress.org/plugins/metadata/managing-post-metadata/#hidden-custom-fields

[cbravobernal]

I'll take this one.

[cbravobernal]

It is solved with a temporary fix, but we should move that logic to the server as mentioned here: #64618 (review)