refactor(dev-infra): Add support for groups in the conditions evaluator (#38164)

Conditions can refer to the groups array that is a list of the preceding groups.
This commit adds support to the verification for those conditions.

This commit also adds some tests to the parsing and condition matching
to ensure everything works as expected.

PR Close #38164

dev-infra/pullapprove/parse-yaml.ts

@@ -6,6 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 import {parse as parseYaml} from 'yaml';
+import {PullApproveGroup} from './group';
 
 export interface PullApproveGroupConfig {
   conditions?: string[];
@@ -33,3 +34,12 @@ export interface PullApproveConfig {
 export function parsePullApproveYaml(rawYaml: string): PullApproveConfig {
   return parseYaml(rawYaml, {merge: true}) as PullApproveConfig;
 }
+
+/** Parses all of the groups defined in the pullapprove yaml. */
+export function getGroupsFromYaml(pullApproveYamlRaw: string): PullApproveGroup[] {
+  /** JSON representation of the pullapprove yaml file. */
+  const pullApprove = parsePullApproveYaml(pullApproveYamlRaw);
+  return Object.entries(pullApprove.groups).reduce((groups, [groupName, group]) => {
+    return groups.concat(new PullApproveGroup(groupName, group, groups));
+  }, [] as PullApproveGroup[]);
+}