Do not generate grid-column when configuring grid-column-start or grid-column-end; Similar for grid-row

[RobinMalfait]

This PR fixes an issue where configuring a custom --grid-column-start or --grid-column-end also generated a grid-column utility due to the overlapping namespace.

@theme {
  --grid-column-start-custom: custom-start;
  --grid-column-end-custom: custom-end;
}

Would then generate:

.col-end-custom {
  grid-column: var(--grid-column-end-custom);
}
.col-start-custom {
  grid-column: var(--grid-column-start-custom);
}
.col-start-custom {
  grid-column-start: var(--grid-column-start-custom);
}
.col-end-custom {
  grid-column-end: var(--grid-column-end-custom);
}

Instead of the expected:

.col-start-custom {
  grid-column-start: var(--grid-column-start-custom);
}
.col-end-custom {
  grid-column-end: var(--grid-column-end-custom);
}

This fix is also applied to grid-row when configuring --grid-row-start and --grid-row-end

Fixes: #18906

[philipp-spiess]

I think the same issue exists for --grid-row?

From my WIP PR:

[RobinMalfait]

@philipp-spiess ah yep; I'm sure there are more cases but I still want to fix this in a more generic way somehow.

For now, updated the PR to handle both --grid-column and --grid-row