Generalize source change helpers

[Lythenas]

As a developer and user of the library I want to be able to write functions with more than two arguments and still use easy helper functions to be able to create source changes.

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This means generalizing the following to accept more than 1/2 values (in the forward direction):

• unary_num_reverse, binary_num_reverse
• UnaryNumericFunctionHelper, BinaryNumericFunctionHelper
• CallContext::unary_numeric_arg_helper, CallContext::binary_numeric_arg_helper

[Lythenas]

This might not actually be that good because this will also affect origins and it is easy to work with Unary/BinaryOrigin.