chore(compiler): improve typescript compiler

[ahnpnl]

Related to #1310, #1146

What has changed

• A new folder compiler is introduced. This folder contains an entry point instance.ts which takes care of using different typescript apis to compile ts file: either LanguageService, Program or isolatedModule.

• Each way of using typescript apis has its own respected files.

• Most of the codes in the old file compiler (for Language Service and transpile module) were kept and moved to their own respected files (language-service.ts or transpile-module.ts)

• Improve performance when compiling with LanguageService, thanks to great idea from Implement getProjectVersion TypeStrong/ts-node#963 (improvement for RFC: Performance report for each ts-jest version  #1115 and all related issues mentioned there).

• Remove getTypeInfo since this is not used. Perhaps if someone needs it, we can add it again.

• Introduce new option in ts-jest config: compilerHost. This option will allow users to use typescript Program or Incremental Program to compile ts files.

What can be done further after this ?

• Try out separating emit typescript diagnostics into another node process using worker, see https://github.com/microsoft/TypeScript/wiki/Performance#concurrent-type-checking

• Since introducing Program or Incremental Program, we need to get feedbacks from community. LanguageService should still work normally.

[coveralls]

Pull Request Test Coverage Report for Build 4087

• 200 of 207 (96.62%) changed or added relevant lines in 5 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.09%) to 91.628%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/compiler/instance.ts	71	72	98.61%
src/compiler/language-service.ts	58	59	98.31%
src/compiler/program.ts	60	65	92.31%

Totals
Change from base Build 4085:	-0.09%
Covered Lines:	1135
Relevant Lines:	1180

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💛 - Coveralls

[kulshekhar]

This was a big one to review!

Nice PR @ahnpnl 🙂

[ahnpnl]

I haven't updated docs for this PR so there will be another PR for that. Besides, right now IncrementalProgram is used when user enables incremental in tsconfig. However, not all frameworks have supported it yet, e.g. Angular , I think the switch should be a different one.