Add rule 35: Expensive Operator, for an operator with at least 20% of a statement's time and no other finding #4527

Part of #4511, the sync of plan analysis changes from PerformanceStudio (PS) to PerformanceMonitor (PM). Needs #4513 and #4515 first.

PS rule 35 shows a costly operator that no other rule has advice for. It fires when an operator's own time is at least 20% of the statement's elapsed time and the operator has no other warning. The statement must have run for at least 1,000 ms. In a statement of a few milliseconds, one or two operators hold most of the time, so the share means nothing. Severity is Critical at 50% or more, else Warning, and the benefit is the self-time share.

erikdarlingdata/PerformanceStudio@e05bc69 adds the rule, and erikdarlingdata/PerformanceStudio@0ba9135 (erikdarlingdata/PerformanceStudio#562) adds the 1,000 ms floor. PM has no rule 35. Size S.

Port it after the two self-time fixes. Before those fixes, the rule flags operators whose self-time is wrong, such as an exchange above a batch mode zone.

At 1899737f. dev has no later change to PerformanceMonitor.PlanAnalysis.