View only routes importing incorrectly

**I'm submitting a bug report**

* **Library Version:**
2.2.1

**Please tell us about your environment:**
* **Operating System:**
Windows 8.1

* **Node Version:**
10.8.0

* **NPM Version:**
6.2.0

* **JSPM OR Webpack AND Version**
webpack 4.16.5

* **Browser:**
all
* **Language:**
TypeScript 3.01

**Current behavior:**

When directing to html templates as module id in routes:
`
routes = [{
moduleId: PLATFORM.moduleName('foo.html'),
}]
`

`this._import(moduleId, defaultHMR)` in method `loadModule` in `WebpackLoader` returns rejected promise with value `Error: Unable to find module with ID: ./foo.html at WebpackLoader`

**Expected/desired behavior:**

* **What is the expected behavior?**

Everything works correctly if `.html` suffix is omited and new file foo.ts with empty class inside it is created.

According to feature https://github.com/aurelia/templating-router/pull/25 using only html views should work. Implementation of this feature was done by dynamically creation empty of class and it seems that loader is not aware of it happening.

Start at the WebpackLoader.loadModule method and its this._import(moduleId, defaultHMR) call. Reproduce the route using PLATFORM.moduleName('foo.html') with webpack 4.16.5, then trace how the dynamically created empty class is handled. Done means an HTML-only route imports successfully without creating a foo.ts file.

Written by the indexing model from the issue text.