This PR fixes the upgrade tool by properly migrating the
`leading-[<number>]` classes.
The issue is that `leading-[<number>]` maps to the number directly, but
if you use a bare value, then it's a multiplier for based on the
`--spacing` value.
E.g.:
*leading-[2]*:
```css
.leading-\[2\] {
--tw-leading: 2;
line-height: 2;
}
@property --tw-leading {
syntax: "*";
inherits: false;
}
```
*leading-2*:
```css
.leading-2 {
--tw-leading: calc(var(--spacing) * 2);
line-height: calc(var(--spacing) * 2);
}
@property --tw-leading {
syntax: "*";
inherits: false;
}
```
This PR will now prevent migrating arbitrary values to bare values for
`leading-*` utilities.
That said, this does introduce a small improvement where `leading-[1]`
is migrated to `leading-none`.
Fixes: https://github.com/tailwindlabs/tailwindcss/issues/15924
3da9d61371