Adjust incrementalCompilationCachingBasic to reproduce issue 88113

[hjyamauchi]

Need to not use load module interface to reproduce issue 88113 and add a note that it needs to be fixed with prefix mapping enabled.

[hjyamauchi]

@swift-ci please test

[cachemeifyoucan]

Prefix mapping incremental build is not working great right now. I have a fix but I was waiting for rewriting the tests to land it so I don't need to write test again. Let me post that.

[hjyamauchi]

ok. I thought it'd be good to keep the regression test coverage for the incremental build issue. I can hold this off (or maybe ask you to incorporate this PR into your change) as you are reworking the tests? What do you prefer?

[cachemeifyoucan]

#2128

I rewrite the incremental tests to swift testing so it is easy to spot any tests have different behavior.

[hjyamauchi]

I confirmed that #2128 fixes this test for the cachingPrefixMapped config. Thank you. I updated this PR just to change the test to not to use -module-load-mode prefer-interface to reproduce the issue 88113. Are you open to that?

[cachemeifyoucan]

We need to make sure we have coverage for both. In general, we shouldn't use this flag to control the coverage, but using inputs that are interface-only or binary module only to ensure the coverage.