analyzer: add plugin severity and dep-overrides to options signature

This was omitted from https://dart-review.googlesource.com/c/sdk/+/447540.

If a user (or me) changes the dependency_overrides section of
plugins options, we should refresh analysis.

Change-Id: I74251412a089bf8a73e530faefead6c28a1fdbae
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/447608
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: srawlins

pkg/analyzer/lib/src/dart/analysis/analysis_options.dart

@@ -604,7 +604,10 @@ class AnalysisOptionsImpl implements AnalysisOptions {
             in pluginConfiguration.diagnosticConfigs.values) {
           buffer.addString(diagnosticConfig.group ?? '');
           buffer.addString(diagnosticConfig.name);
-          buffer.addBool(diagnosticConfig.isEnabled);
+          buffer.addInt(diagnosticConfig.severity.index);
+        }
+        if (pluginsOptions.dependencyOverrides case var dependencyOverrides?) {
+          buffer.addString(dependencyOverrides);
         }
       }