Allow overridable method delegation in downstream CompilerOpts implementations

[prozacchiwawa]

This adds an interposer which allows a CompilerOpts to be implemented as a wrapper around an existing CompilerOpts object and allows the user simultaneously to provide individual method overrides only where desired. This allows the interface for CompilerOpts to grow and change without imposing as much on downstream implementations. CompilerOpts provides file reading (and writing and file dates in the module system pr) which are used to delegate these functions in uncommon scenarios such as when we want to test how the compiler reacts to the presence or absence of files, or collect multiple outputs without writing to disk. The HasCompilerOptsDelegation trait has methods which provide default implementations for every method of CompilerOpts, but which the user can replace when they implement HasCompilerOptsDelegation. Having HasCompilerOptsDelegation automatically gives one a trait implementation for CompilerOpts which uses those overrides.

[coveralls]

Pull Request Test Coverage Report for Build 8820477360

Details

• 108 of 174 (62.07%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage decreased (-0.2%) to 82.812%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/compiler/comptypes.rs	108	174	62.07%

Files with Coverage Reduction	New Missed Lines	%
src/compiler/sexp.rs	1	80.73%

Totals
Change from base Build 8805170223:	-0.2%
Covered Lines:	15047
Relevant Lines:	18170

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💛 - Coveralls