Differentiate size `m` and `l` on `EuiSpacer`

[ryankeairns]

I don't know how long it has been this way, but m and l are both 16px. Large should be 24px.

[DevLikhith5]

Both m (16px) and l were resolving to the same size. This ensures l is always 1.5x the base (24px).