V2 API

[tothambrus11]

This PR changes the API so that LLVM reference types no longer look like regular value-semantic objects. The wrappers themselves remained nearly identical, but all methods have been modified to return and take UnsafeReference's to objects of given type, which can be dereferenced via .unsafe[].

The new UnsafeReference type also allowed us to get rid of existentials, and implement a pseudo-subtyping of references through conversion initializers and .erased between AnyType and T: IRType, between AnyValue and T: IRValue, and between AnyAttribute and attribute types.

To reduce the need for .erased in functions that accept AnyValue/AnyType, I modified functions to accept UnsafeReference<some IRType/IRValue>. In case of functons with collection inputs, I added overloads with generic variadic tuple parameters, which are internally type-erased and forwarded to the erased overload. Since AnyType is IRType and AnyValue is IRValue, the tuple based overload works even if some of the arguments are type-erased already.

I completed adding docs for all symbols, looking at LLVM docs where needed. I also added links to the relevant LLVM docs for all intrinsics.

To review the usability of the new API, take a look at hylo-lang/hylo-new#53

[codecov]

Codecov Report

❌ Patch coverage is 84.12538% with 157 lines in your changes missing coverage. Please review.
✅ Project coverage is 84.32%. Comparing base (591ab6e) to head (a9cb4b7).

Files with missing lines	Patch %	Lines
Sources/SwiftyLLVM/Module.swift	80.88%	78 Missing ⚠️
Sources/SwiftyLLVM/Refs.swift	55.17%	26 Missing ⚠️
Sources/SwiftyLLVM/Types/FloatingPointType.swift	72.72%	12 Missing ⚠️
Sources/SwiftyLLVM/Attribute.swift	50.00%	9 Missing ⚠️
Sources/SwiftyLLVM/Utils/Unreachable.swift	0.00%	7 Missing ⚠️
Sources/SwiftyLLVM/Backend.swift	85.71%	5 Missing ⚠️
Sources/SwiftyLLVM/AtomicOrdering.swift	62.50%	3 Missing ⚠️
Sources/SwiftyLLVM/TargetMachine.swift	82.35%	3 Missing ⚠️
Sources/SwiftyLLVM/OptimizationLevel.swift	86.66%	2 Missing ⚠️
Sources/SwiftyLLVM/Types/VoidType.swift	66.66%	2 Missing ⚠️
... and 7 more

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #112       +/-   ##
===========================================
+ Coverage   69.20%   84.32%   +15.11%     
===========================================
  Files          50       54        +4     
  Lines        1117     1435      +318     
===========================================
+ Hits          773     1210      +437     
+ Misses        344      225      -119     

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[kyouko-taiga]

I don't understand the changes that have been made in C++ files.

I'm not super convinced about the way entity stores work and would prefer if we found a more efficient way to track how entities are being borrowed. I am also not a fan of the pattern using constructor to create temporary objects. I think we should use higher-order functions to that effect.

[tothambrus11]

@kyouko-taiga Can we merge this?