Replace newTranslatableError with UserFriendlyError (#10440

* Introduce UserFriendlyError

* Replace newTranslatableError with UserFriendlyError

* Remove ITranslatableError

* Fix up some strict lints

* Document when we/why we can remove

* Update matrix-web-i18n

Includes changes to find `new UserFriendlyError`,
see https://github.com/matrix-org/matrix-web-i18n/pull/6

* Include room ID in error

* Translate fallback error

* Translate better

* Update i18n strings

* Better re-use

* Minor comment fixes

package.json

@@ -28,7 +28,7 @@
     "matrix_lib_main": "./lib/index.ts",
     "matrix_lib_typings": "./lib/index.d.ts",
     "matrix_i18n_extra_translation_funcs": [
-        "newTranslatableError"
+        "UserFriendlyError"
     ],
     "scripts": {
         "prepublishOnly": "yarn build",
@@ -203,7 +203,7 @@
         "jest-mock": "^29.2.2",
         "jest-raw-loader": "^1.0.1",
         "matrix-mock-request": "^2.5.0",
-        "matrix-web-i18n": "^1.3.0",
+        "matrix-web-i18n": "^1.4.0",
         "mocha-junit-reporter": "^2.2.0",
         "node-fetch": "2",
         "postcss-scss": "^4.0.4",