Per-rule severity overrides keyed by RuleNumber (needs analyzer configuration first) #4535

Part of #4511, the sync of plan analysis changes from PerformanceStudio (PS) to PerformanceMonitor (PM). Needs #4520.

PS lets a user change the severity of each rule's findings. erikdarlingdata/PerformanceStudio@dcc06db (erikdarlingdata/PerformanceStudio#575) stamps PlanWarning.RuleNumber on every finding and keys the override on it. Before that fix, overrides matched through a table of warning type names. That table missed rules 34 to 37 and 39, two of rule 30's three finding types, and rule 10's RID Lookup. Overrides skip SQL Server's own warnings, which needs the Source field from #4520.

PM has no AnalyzerConfig, and Analyze takes no configuration (PlanAnalyzer.cs:23). So RuleNumber has no use in PM until PM adds per-rule configuration. Size L.

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