[Decompiler] Fix up pretty printing and other small changes

[water111]

This fixes most of the pretty printing problems. The remaining issues are:

• Pretty printing's greedy algorithm may still be ugly in cases where many line breaks must be automatically inserted
• If we have to split a form like (+ a (-> <something-huge>)), we will insert a line break in between + and a, when it is likely better to only break after a. We should define "sticky forms" that like to keep their first argument, if it is possible.

Minor tweaks

• Recognize and eliminate extra temporaries inserted by GOAL abs macro.

[coveralls]

Pull Request Test Coverage Report for Build 628404450

• 121 of 145 (83.45%) changed or added relevant lines in 11 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.04%) to 68.717%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
decompiler/analysis/cfg_builder.cpp	2	3	66.67%
decompiler/analysis/inline_asm_rewrite.cpp	0	2	0.0%
decompiler/analysis/insert_lets.cpp	19	21	90.48%
decompiler/IR2/IR2_common.h	2	6	33.33%
decompiler/analysis/final_output.cpp	0	4	0.0%
decompiler/IR2/FormExpressionAnalysis.cpp	51	62	82.26%

Totals
Change from base Build 628336906:	0.04%
Covered Lines:	31767
Relevant Lines:	46229

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💛 - Coveralls