File replacements work only for TypeScript files

[sis0k0]

Bug Report or Feature Request (mark with an x)

- [ ] bug report -> please search issues before submitting
- [X] feature request

Area

- [X] devkit
- [ ] schematics

Versions

node: v9.9.0
npm: v5.8.0
OS: Fedora 25

Repro steps

https://github.com/sis0k0/ng-webpack-vfs-issue/

Desired functionality

The file replacement functionality should work for all types of files.
Currently, the file replacement functionality works only for TS files. More specifically - it works only for files that are part of the webpack compiler host.
Also, the webpack input filesystem host that's provided as an option of the AngularCompilerPlugin doesn't intercept any requests to html and css files or external packages, which contain JS (not TS) files.

Mention any other details that might be useful

That behavior is caused by the following method invocations, which turn off the usage of the provided host:

devkit/packages/ngtools/webpack/src/virtual_file_system_decorator.ts

Line 23 in e335e5d

if (this._webpackCompilerHost.fileExists(path, false)) {

devkit/packages/ngtools/webpack/src/virtual_file_system_decorator.ts

Line 31 in e335e5d

if (this._webpackCompilerHost.fileExists(path, false)) {