As of #23867 this is now a real package, so updating the imports to
use the real package name, rather than relying on the alias. The
name change in the package name is because `I18n` is not a valid
name as NPM packages must be all lowercase.
This commit also introduces an eslint rule to prevent importing from
the old I18n path.
For themes/plugins, the old 'i18n' name remains functional.
Adds a new `[grid]` tag that can arrange images (or other media) into a grid in posts.
The grid defaults to a 3-column with a few exceptions:
- if there are only 2 or 4 items, it defaults to a 2-column grid (because it generally looks better)
- on mobile, it defaults to a 2-column grid
- if there is only one item, the grid has no effect
