Split streaming submitButtonDisabled computed prop into multiple props

The following discussion from !132603 (merged) should be addressed:

• @jmontal started a discussion: (+1 comment)

  question (non-blocking): If I'm understanding this correctly we have 4 different paths isSubmitButtonDisabled() can go through in which two cases enable the button, and two cases disable the button?

  WDYT about moving each of these checks/cases to computed methods to clarify what case enables/disables the button?

  This could also be a follow up issue as I've marked it non-blocking for now as our other editors follow the same pattern