Support short blocks in #[] operator call's macro interpolation

[HertzDevil]

Before:

foo.[](&.bar)
foo.[]?(x: 1, &.bar)
foo.[]=(2, 3, y: 4, &.bar)

After:

foo[&.bar]
foo[x: 1, &.bar]?
foo[2, y: 4, &.bar] = 3

[ysbaddaden]

A part of me thinks this is lovely, but the part is afraid of reading any code doing that (either the before or after versions). I have zero idea what they do.

[straight-shoota]

The bracket syntax is already supported. This PR is just filling in support for short blocks. It might not be super useful, but it's solid. So there's not reason not to do this.

The assignment operator variant especially seems very weird, I agree on that 😆