feat: Tree component

[ThisIsDemetrio]

Description

We add the Tree component, based on Ant Design Tree component.

Includes most of the properties of the original Tree component, like: showing vertical lines for chidlren, showing icons before the node, checkbox on nodes, strict checking, callback on checking (by clicking the checkbox, if enabled) and/or on selecting item (by clicking on the name), fixed height and virtual scrolling.

Add a little tweak to ensure that, when showing lines, the icon to expand/collapse children is still a caret (and not the "+"/"-" icons).

Also:

• updated Tree tokens and Global tokens to be sure the right colors are shown based on the configured theme. Because of this, the Palette type has been expanded to include the text property
• updated the theme because of some updates on the Neutral primitives (for consistency on tree nodes hovering)

Addressed issue

No particular issue opened for this component.

Checklist

• [X] commit message and branch name follow conventions
• [X] tests are included
• [X] changes are accessible and documented from components stories
• [X] typings are updated or integrated accordingly with your changes
• [X] all added components are exported from index file (if necessary)
• [X] all added files include Apache 2.0 license
• [X] you are not committing extraneous files or sensitive data
• [X] the browser console does not have any logged errors
• [X] necessary labels have been applied to this pull request (enhancement, bug, ecc.)

[fredmaggiowski]

since we changed existing theme colors, is this breaking?

the next tag will already include color changes, i'm labelling this as breaking as well