Implement an explicit error message

[charpeni]

Summary

Improve error messages for toBeAny(), toBeString(), toBeNumber(), and other type assertion methods to clearly show expected vs actual types

Fixes #179

Before

error TS2349: This expression is not callable.
  Type 'ExpectAny<2>' has no call signatures.

After

error TS2349: This expression is not callable.
  Type '{ "Expected: any, Actual: literal number: 2": never; }' has no call signatures.

For negated assertions:

error TS2349: This expression is not callable.
  Type '{ ".not.toBeAny() failed; Actual: any": never; }' has no call signatures.

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/mmkal/expect-type@189

commit: 66decd2

[mmkal]

I'm not against this - these messages are probably less intimidating for people who aren't yet familiar. Some feedback for this PR to be complete (though I'll still want to think about whether this is definitely better and also whether it should be considered a breaking change):

1. Could you find the parts of the documentation that specifically reference the Type 'ExpectString<number>' has no call signatures kind of messages (bonus: see if there's some similar documentation in vitest?)
2. We now have several types (like ExpectString) that are not used, I believe. If so, these should be removed. Once we can see what removing them looks like we can consider whether this would be a breaking change. (Probably not, as it's documented under "Internal Type Helpers" that these types might be removed without a major bump)