make organize imports more flexible about import placement

[Techatrix]

The current implementation of source.organizeImports (#2051) always places the imports at the top of the file. Sometimes you find code that has all imports at the bottom of the file or some imports between code. It would be nice if ZLS could handle this.

I can think of two possible solutions:

1. add a special case where ZLS will place all imports at the bottom of the file (no config option)
2. never move imports to a different location, only sort imports that are next to each other i.e. not separated by an empty line

The first solution has been implemented #2391. I am going to keep this issue open as there may still be viable to implement the second solution.

[Srekel]

+1 to keeping imports together.

Here is an example where it's moved lines from the second "paragraph" of consts into the first paragraph of imports. I like to group imports by having a space inbetween.

[nihklas]

Why not making it configurable? I think it would help enforce code style beyond what zig fmt does. I don't know how common it is to have imports both at the top and the bottom in the same codebase.