sql/opt: add implicit SELECT FOR UPDATE support for DELETE statements

[nvanbenschoten]

Address this TODO:

cockroach/pkg/sql/opt/exec/execbuilder/mutation.go

Lines 991 to 999 in 01a780b

	// tryApplyImplicitLockingToDeleteInput determines whether or not the builder
	// should apply a FOR UPDATE row-level locking mode to the initial row scan of
	// an DELETE statement.
	//
	// TODO(nvanbenschoten): implement this method to match on appropriate Delete
	// expression trees and apply a row-level locking mode.
	func (b *Builder) shouldApplyImplicitLockingToDeleteInput(del *memo.DeleteExpr) bool {
	return false
	}

Similar to #50180, but likely lower priority because sustained contending DELETEs don't seem to be as common, probably because once a row is deleted, it stays deleted and can't be deleted again.

Jira issue: CRDB-4147

[rytaft]

Is this a priority for 22.2?

[michae2]

This might be a good one for @wenyihu6 if interested.

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