Make experimental speed changes standard and add esbuild plugin

[maier49]

Type: feature

The following has been addressed in the PR:

• There is a related issue
• All code has been formatted with prettier
• Unit or Functional tests are included in the PR
• schema.json has been updated appopriately

Description:
This moves the "experimental" speed features into the standard development build where possible, also adding esbuild to replace the ts-loader.

• Has essentially no effect on the production build, but cuts dev build times in half for a large project (from about 85 seconds to about 45 seconds) .
• On a fresh project from cli-create-app dev build times went from 9-10 seconds to 7-8 seconds.
• Checked source maps for dev and dist builds and they seem fine.
• On repeated builds, including the hard source webpack plugin initially cut times down but the build time grew continuously on every subsequent builds. If that issue can be tracked down (I didn't see anything in their issues) then it could cut these times down further
• We were previously removing the postcss config when the experimental speed flag was on. However, we've enabled nesting selectors in our css config. So removing that broke builds that otherwise would be fine, either by failing in BTR or simply breaking styles in the app.

Resolves #217

[agubler]

Does BTR always need to be "sync" with these changes?

[maier49]

I'm not positive whether BTR breaks if it's async for a single bundle. Since the dev build here is now always a single bundle I just converted all the single bundle conditionals to true.

[maier49]

BTR is still async unless singleBundle is explicitly set to true for the dist build, if that wasn't clear.

[agubler]

Closing this PR, there is basic support for esbuild now and there are signifiant conflicts. However some of these changes will need to be considered when re-visiting the performance issue #217