[Enhancement] Support TS for indexTransform

[vixnguyen]

PR Checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Build related changes

What is the current behavior?

Issue Number: #687

Does this PR introduce a breaking change?

• No

[just-jeb]

Thanks for contribution! Overall looks good, left a few comments please address them.
Also please add and e2e test. You should test the specific use case that was failing (no webpack.config defined in angular.json but indexTransform is defined and it's a TS file).
The best way to do that is:

1. Add another configuration in this that defines indexTransform with TS file but not custom webpack config.
2. Add a test case similar to this but with corresponding configuration name.
3. Add a protractor config similar to this but with the appropriate spec name. Also, instead of specs.push use `specs = ['your-regex'].
4. Add a run for this e2e test in the ci script while using --configuration=your-config option instead of --prod.

[just-jeb]

Thanks for the great job! Just two more comments to address and I'm merging.

[just-jeb]

Since it's a TS example we should showcase the types usage here.
Please import the relevant types from @angular-builders/custom-webpack (if needed then reexport from @angular-devkit).

[vixnguyen]

In my opinion, use static type for indexHtml is good, but the other one is unnecessary, try to import a type and use for readonly obj just make our code more complicated. So, in that case, I think write document(readme) for it is enough.

[just-jeb]

I disagree, having a type for these options is very helpful and gives you the exact set of options you can use. Otherwise you should go back and forth to the documentation (given it's up to date).
If it's a problem I can add the type myself.

[vixnguyen]

Haha. It's no problem to me 😄 , just discuss and raise my concerns. Moreover, you are the owner, you can ask me to do everything because I happy to contribute to your package and willing to follow your rules. So don't talk to me that way If it's a problem I can add the type myself..

[vixnguyen]

And one more concern, I think indexHtml is more important than targetOptions, so it should be the first param, some cases we no need to use targetOptions. Is it possible to have a breaking change in the next release?

[vixnguyen]

@just-jeb Please help me to check again. Thanks!

[just-jeb]

All good, merging!
Btw, what is itwcw exactly?

[just-jeb]

@all-contributors please add @vixnguyen for code.

[allcontributors]

@just-jeb

I've put up a pull request to add @vixnguyen! 🎉

[vixnguyen]

@just-jeb
itwcw stand for Index Transform without Custom Webpack