Issue #3053890: SubformState should complain when the subform doesn't have #tree = TRUE

Closes #3053890

added 210 commits

• 2c43e466...bfce4567 - 205 commits from branch project:11.x
• 3c05cd7a - If the subform's #tree property is not set in the createForSubform method of...
• ae45030c - Fixed unit tests.
• 318ed40f - Changed wording of docs.
• b427f48f - Added test for exception.
• 4ae90903 - Fixed missing #tree in field config form.

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