Allow selection in readonly mode

[acywatson]

I've come full circle on this, and now I think the best idea here is to allow programmatic updates of the editor state regardless of the value of editor._readOnly. In attempting to implement something in the core that would stop programmatic updates by default and allow overriding that for specific updates via an update option, the intent was to make it easy for people to convert their editors into static content without having to worry about adding separate conditionals in all the places where programmatic updates can be triggered.

Practically, there are a lot of challenges with implementing this in the core. Command listeners are implicitly wrapped in a single editor.update, which causes a lot of problems with trying to apply behavior-changing modifiers (like options or tags) to individual "updates". We can't decouple command listeners from updates because batching can make updates async, which makes it hard to get the return value out of the update closure. It also seems like tags are broken with batching in general, as batched changes will all have the same tag applied to them.

From a conceptual standpoint, it probably makes just as much sense to make this a concern of the UI and/or the Lexical consumer as it does to try to bake a semantic guarantee around updates into the core.

This PR just takes out the check that prevents us from tracking Selection in readOnly mode, which will allow things like Commenting to work in that case.

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[zurfyx]

Stamp to unblock but I think @trueadm should have a word on this because he was touching these conditions just recently

[trueadm]

Do we need any changes in LexicalEvents too, around selectionchange? Also what about copy events, should we let them through still?

[acywatson]

Do we need any changes in LexicalEvents too, around selectionchange?

I don't think so? Did you have something specific in mind?

Also what about copy events, should we let them through still?

We can, but it's not important for this to work. AFAICT. Currently, copying still works, it's just plain/text and HTML on the clipboard. If we want to put the native Lexical format on there, we can change how readOnly is handled in LexicalEvents later.

[trueadm]

FWIW this is definitely a breaking change – so we should include this in the 0.4 release.