perf(transformer): remove createProgram from transpiler

[zhming0]

Summary

I found that Typescript's createProgram API is called even when isolatedModule is set.
This is a major slow down (100 msecs vs 10~50 secs) for test start up and it doesn't seem to make sense for isolatedModule anyway.
Longer test start up -> longer feedback cycle -> lower productivity.

Test plan

N/A. The program isn't used by any part of ts-jest, at least not in its critical path.

Does this PR introduce a breaking change?

• Yes
• No
• Maybe

I just don't know enough about the use case of program for isolatedModule.

Other information

I tried to gather the history around this but couldn't find any notes regarding transpiler's need for program.
If the createProgram turned out to be desirable thing here, I am happy to create another PR to introduce a flag to disable it.

Otherwise, I believe majority of isolatedModule users will benefit from this PR greatly.

[ahnpnl]

this is strange, unless something call program.emit() will trigger something, I didn't notice there is downgrade performance with isolatedModules: true when createProgram is called.

The reason why createProgram is there because in custom AST transformers, some might want to access to the internal Program that ts-jest is using. However, since transpile API is used for isolatedModules: true, createProgram might not make any sense.

I agree that we can remove it.

[coveralls]

Pull Request Test Coverage Report for Build 5859

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.003%) to 93.367%

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Totals
Change from base Build 5857:	-0.003%
Covered Lines:	1132
Relevant Lines:	1166

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💛 - Coveralls