Custom ESLint rules to enforce new ThemedComponent selector convention

The following cases are covered:
- ThemedComponent wrapper selectors must not start with ds-themed-
- Base component selectors must start with ds-base-
- Themed component selectors must start with ds-themed-
- The ThemedComponent wrapper must always be used in HTML
- The ThemedComponent wrapper must be used in TypeScript _where appropriate_:
  - Required
    - Explicit usages (e.g. modal instantiation, routing modules, ...)
    - By.css selector queries (in order to align with the HTML rule)
  - Unchecked
    - Non-routing modules (to ensure the components can be declared)
    - ViewChild hooks (since they need to attach to the underlying component)

All rules work with --fix to automatically migrate to the new convention
This covers most of the codebase, but minor manual adjustment are needed afterwards

lint/test/testing.ts

@@ -0,0 +1,52 @@
+/**
+ * The contents of this file are subject to the license and copyright
+ * detailed in the LICENSE and NOTICE files at the root of the source
+ * tree and available online at
+ *
+ * http://www.dspace.org/license/
+ */
+
+import { RuleTester } from 'eslint';
+import { RuleTester as TypeScriptRuleTester } from '@typescript-eslint/rule-tester';
+import { themeableComponents } from '../src/util/theme-support';
+
+const FIXTURE = 'lint/test/fixture/';
+
+// Register themed components from test fixture
+themeableComponents.initialize(FIXTURE);
+
+TypeScriptRuleTester.itOnly = fit;
+
+export function fixture(path: string): string {
+  return FIXTURE + path;
+}
+
+export const tsRuleTester = new TypeScriptRuleTester({
+  parser: '@typescript-eslint/parser',
+  defaultFilenames: {
+    ts: fixture('src/test.ts'),
+    tsx: 'n/a',
+  },
+  parserOptions: {
+    project: fixture('tsconfig.json'),
+  }
+});
+
+class HtmlRuleTester extends RuleTester {
+  run(name: string, rule: any, tests: { valid: any[], invalid: any[] }) {
+    super.run(name, rule, {
+      valid: tests.valid.map((test) => ({
+        filename: fixture('test.html'),
+        ...test,
+      })),
+      invalid: tests.invalid.map((test) => ({
+        filename: fixture('test.html'),
+        ...test,
+      })),
+    });
+  }
+}
+
+export const htmlRuleTester = new HtmlRuleTester({
+  parser: require.resolve('@angular-eslint/template-parser'),
+});