[Decompiler] Begin expression conversion, rearrange tests

[water111]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 506337060

• 555 of 632 (87.82%) changed or added relevant lines in 18 files are covered.
• 2 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.07%) to 65.72%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
decompiler/Function/TypeAnalysis.cpp	1	2	50.0%
decompiler/IR2/FormStack.cpp	10	11	90.91%
decompiler/ObjectFile/ObjectFileDB_IR2.cpp	0	1	0.0%
decompiler/analysis/expression_build.cpp	14	18	77.78%
test/decompiler/FormRegressionTest.cpp	81	86	94.19%
decompiler/IR2/FormExpressionAnalysis.cpp	108	116	93.1%
decompiler/IR2/Form.cpp	28	85	32.94%

Files with Coverage Reduction	New Missed Lines	%
decompiler/ObjectFile/ObjectFileDB_IR2.cpp	1	0%
goalc/listener/Listener.cpp	1	84.19%

Totals
Change from base Build 505130709:	0.07%
Covered Lines:	24961
Relevant Lines:	37981

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💛 - Coveralls

[water111]

I ended up rearranging a bunch of test stuff instead of doing much work on expressions. Merging this as a separate PR so the expression stuff is easier to look at.