Print deprecation warnings on deprecated method argument

[ysbaddaden]

We can annotate a method argument, which means we can technically put the @[Deprecated] annotation to deprecate a method argument, but there was no incentive to do it... yet.

In #15924 we want to deprecate a specific method argument (blocking) and we can't use the usual duplicated methods, one with the argument (deprecated) and another one without it, because it too many cases this is a positional argument, and it comes after other positional arguments with a default value.

This PR adds deprecation checks for method arguments, and prints a warning when an argument is deprecated. For example:

def foo(a, b = nil, @[Deprecated] c = nil)
end

foo(1)
foo(1, 2)
foo(1, 2, 3)
foo(1, c: 3)

Will generate the following deprecations, only complaining when we pass an explicit value to the deprecated argument (the first two calls are fine, the last two are not):

In x.cr:6:11

 6 | foo(1, 2, 3)
               ^
Warning: Deprecated argument c.

In x.cr:7:11

 7 | foo(1, c: 3)
               ^
Warning: Deprecated argument c.

A total of 2 warnings were found.

See the specs for all the different cases, inclusing splats, and double splats.

The PR also fixes a couple pre-requisites, for example making sure that each arg annotation is correctly copied when expanding or duplicating a def, or that the original name of an arg is also carried over, so we don't complain about argument __temp_1 being deprecated.

[Blacksmoke16]

Glad to see another solid use case for annotations on parameters! Good stuff!

[straight-shoota]

Sorry for the pedantic nagging: I'd prefer to extract some of the changes into separate PRs. Especially the first two commits with bugfixes should be merged individually.
I suppose the rest can be together as part of this feature.

[ysbaddaden]

Hum, I should add specs for .new and #initialize too, that don't follow the same path for special arg expansions (and #initialize is expanded as .new too).

[ysbaddaden]

Of course, the #initialize to .new expansions only works partially (positional args are working, but named args, splats and double splats don't)

[ysbaddaden]

Now with fix from #16013 and specs for expansion of #initialize to .new default arguments.

[ysbaddaden]

I'll rebase or merge when the 3 dependent fixes are reviewed and merged: #16007, #16008 and #16013.

[ysbaddaden]

I fixed the conflicts with master.