List Block: add justify support

#### Is your feature request related to a problem? Please describe.
Jetpack added support to justified elements in the paragraph block. The suggestion here is to add the same support to other text elements such as the **List block**.

#### Describe the solution you'd like
To offer the same Justify option to the List block (and to other text-based blocks like #14109)

#### Describe alternatives you've considered
None available for a list block.

#### Additional context

User suggestion for WordPress.com in 3844744-zen

Start by locating the List block implementation and the existing paragraph-block support for justified elements. Compare how the Paragraph block exposes the Justify option, then confirm the List block offers the same control and behavior; the issue does not name specific files or tests.

Written by the indexing model from the issue text.