refactor: deprecate xy-cell-static() and use xy-cell() to generate classes

refactor: deprecate xy-cell-static() and use xy-cell() to generate classes

Deprecate the` xy-cell-static()` mixin and use `xy-cell()` mixin to generate the XY Grid static classes.

The new arguments of `xy-cells` (added in previous commits) have the following goal: making a clear distinction between cells that should not have any gutter, cells from which the gutter must be removed and cells that should have a gutter but generated seperately/later. See migration notes below.

Changes:
- Add deprecation warning in `xy-cell-static()`
- Add deprecation note in `xy-cell-static()` documentation
- Use `xy-cell()` instead of `xy-cell-static()` with the transformations listed below

Migration notes:
- Use `$output: (...)` instead of separate calls to `xy-cell-static()` and `xy-cell-base()`. This may change in the future with 3 distinguish mixins to generate "base", "size" and "gutters" of the cell.
- Use `$gutter-type: none` for cells without gutters
- Use `$gutters: 0` for cells with a 0-width gutters
- Use `$output: (...)` without "gutters" for cells with gutters that must be generated seperately.
- Remove useless `$breakpoint: $-zf-size` as it is always detected automatically