Implement sha and rand

[qmuntal]

This PR has the following changes (review commit by commit):

• ae520e3d9f3fc73b36da3c874f5e0391df3d5c8d: Implements a tool to generate syscall wrappers without having golang.org/x/sys as runtime dependency, which will facilitate vendoring this package into our Go fork. Read inline documentation for more context.
• b5206131e55607106144f05f725b3370f17f1316: Implement all SHA algorithms except SHA224, which is not supported by BCrypt.
• ab022d0501ddc9ca9506b8e808020bed5f2fd141: Implement random number generator.
• ca9c71cfc1353eb4777130f5b2f9c6e6149b8755: Add GH Actions test workflow

[qmuntal]

@jaredpar you might want to review https://github.com/microsoft/go-crypto-winnative/pull/2/commits/c18affdb2479e9e08bcad5cdfb4c9c52c298b198, which I added after your last review.

It reduces boilerplate and makes the code safer by delegating to the autogenerated code the []byte -> *byte+length arguments transform.

[qmuntal]

I've filled an upstream proposal so we can delegate UTF16 string encoding to the autogenerated code: https://github.com/golang/go/issues/51786