Improved SCSS and TypeScript build

[veler]

Changing the way we build CSS and JavaScript:

Before this PR:

1. Had to open Task Runner Explorer in VS in order to get SCSS and TypeScript built
2. It was easy to forget it when doing a change in a SCSS or TypeScript file.
3. We were not committing the generated CSS and JS, forcing every contributor to build them themselves.

With this PR:

1. We commit the generated CSS and JS.
2. We will only build the SCSS and TypeScript if we detect that a SCSS or TypeScript file is more recent than the generated CSS and JS. The CSS/JS build happens during DevToys.Blazor build.
3. As a consequence, no need to have to rely on Task Runner Explorer, or at least it makes it now optional.

Quality check

Before creating this PR:

• Did you follow the code style guideline as described in CONTRIBUTING.md
• Did you build the app and test your changes?
• Did you check for accessibility? On Windows, you can use Accessibility Insights for this.
• Did you verify that the change work in Release build configuration
• Did you verify that all unit tests pass
• If necessary and if possible, did you verify your changes on:
  • Windows
  • macOS (DevToys 2.0)
  • Linux (DevToys 2.0)