Swaps VCol/VRow spacing system to use gap instead of negative margin hack

This will break a lot of layouts which is why I put the issue on a major milestone not 3.9.0. Still unsure what the impact of this will be, we need to check a bunch of real examples and see if it's possible to make the required changes automatically.

• fix for auto broke it .v-row > .v-col overrides .v-row > [class*='v-col-'], maybe we will need to restore make-col, as CSS ifs nor style queries are available yet
  • once reverted, rework migration (CSS for restoring legacy grid)
• migrate docs (ready to append on a separate branch, chilling until we fix ☝🏼 )

I cleaned it up a bit then broke it more, [class*='v-col-'] still matches .v-col-md-6 so columns with no xs size are full-width instead of 0+grow

• proper test suite is needed, checking breakpoints in playground is tedious

We can push it even more into parsing cols="1 of 5" or cols="1/5".

Following example already works, but is too much noise.

<v-row>
  <v-col cols="1" style="--v-row-columns: 5">1/5</v-col>
  <v-col cols="1" style="--v-row-columns: 5">1/5</v-col>
  <v-col cols="1" style="--v-row-columns: 2">1/2</v-col>
  <v-col cols="1" style="--v-row-columns: 10">1/10</v-col>
</v-row>

It can be a follow-up PR. #22572

The last thing that bothers me is that "auto" all over the docs examples instead of "grow". It should be fixed in master.