Regression in 42490768.

Thanks Nick Pope for much review.

Fixed #29541 -- Fixed Cursor.execute() crash when setinputsizes() is called without arguments wit cx_Oracle 6.4.

Fixed #29449 -- Reverted "Fixed #28757 -- Allowed using contrib.auth forms without installing contrib.auth."

This reverts commit 3333d935 due to
a crash if USERNAME_FIELD isn't a CharField.

Thanks Vinay Karanam for the initial patch.

Thanks Tim Graham for the review.

This reverts commit 27ca5ce1 due to a
regression.

Regression in b8a41a28.

Regression in fdc936c9.