Avoid using `Function` type in custom Matchers where a callback is allowed

[thw0rted]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[X] Bug report  
[ ] Performance issue
[ ] Feature request
[ ] Documentation issue or request
[ ] Support request
[ ] Other... Please describe:

Current behavior

The toHaveText / toHaveExactText matchers allow passing of a callback. Typings look like

        toHaveText(text: string | string[] | Function, exact?: boolean): boolean;
        toContainText(text: string | string[] | Function, exact?: boolean): boolean;
        toHaveExactText(text: string | string[] | Function): boolean;

The docs show how to use the callback form as

expect('.zippy__content').toHaveText(text => text.includes('..'));

This results in a TS7006 error, Parameter 'text' implicitly has an 'any' type -- I think only when compiled with the noImplicitAny flag.

Expected behavior

The typings should specify the correct signature for the calback instead of Function. That's probably (value: string) => boolean, if I understand the way it's meant to work.

What is the motivation / use case for changing the behavior?

Callers should be able to declare a callback without explicit typing.

Environment

Angular version: 11.0.4

[thw0rted]

I made https://github.com/thw0rted/spectator/tree/patch-1 using the online editor but haven't re-run your build/test to see if it breaks anything yet.

(Also: I didn't quite grok your commit-message rules -- what are "type" and "scope"? Are there specific valid values for those laid out somewhere?)