[Decompiler] Test framework for decompiler regression tests and gcommon tests

[water111]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 494266819

• 226 of 246 (91.87%) changed or added relevant lines in 6 files are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+7.1%) to 62.568%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
decompiler/IR2/Form.cpp	0	1	0.0%
decompiler/ObjectFile/LinkedObjectFile.cpp	4	5	80.0%
decompiler/Function/TypeAnalysis.cpp	1	5	20.0%
test/decompiler/test_FormRegression.cpp	197	202	97.52%
decompiler/IR2/variable_naming.cpp	18	27	66.67%

Files with Coverage Reduction	New Missed Lines	%
decompiler/IR2/variable_naming.cpp	1	71.56%

Totals
Change from base Build 492330847:	7.1%
Covered Lines:	24712
Relevant Lines:	39496

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💛 - Coveralls

[water111]

Having this type of test seems very valuable, and I already found a few bugs when creating this. The biggest issue with these tests is it's really confusing to understand the output before all the expression stuff has been properly built (stuff like "hidden variables" set in branch delay slots, the ordering of body/condition in loops, etc). But I think it's still worth it to come up with a set of test functions that we can test at various points in the decompiler, and it will only get easier to add more tests as the decompiler progresses.