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

.eslintrc.json

@@ -11,7 +11,10 @@
     "eslint-plugin-jsonc",
     "eslint-plugin-rxjs",
     "eslint-plugin-simple-import-sort",
-    "eslint-plugin-import-newlines"
+    "eslint-plugin-import-newlines",
+    "eslint-plugin-jsonc",
+    "dspace-angular-ts",
+    "dspace-angular-html"
   ],
   "overrides": [
     {
@@ -238,7 +241,11 @@
           "method"
         ],
 
-        "rxjs/no-nested-subscribe": "off"     // todo: go over _all_ cases
+        "rxjs/no-nested-subscribe": "off",     // todo: go over _all_ cases
+
+        // Custom DSpace Angular rules
+        "dspace-angular-ts/themed-component-selectors": "error",
+        "dspace-angular-ts/themed-component-usages": "error"
       }
     },
     {
@@ -253,7 +260,10 @@
         "createDefaultProgram": true
       },
       "rules": {
-        "prefer-const": "off"
+        "prefer-const": "off",
+
+        // Custom DSpace Angular rules
+        "dspace-angular-ts/themed-component-usages": "error"
       }
     },
     {
@@ -262,7 +272,11 @@
       ],
       "extends": [
         "plugin:@angular-eslint/template/recommended"
-      ]
+      ],
+      "rules": {
+        // Custom DSpace Angular rules
+        "dspace-angular-html/themed-component-usages": "error"
+      }
     },
     {
       "files": [