Enhancement: [calcite-tree-item] limit padding-y CSS var to top/bottom spacing, remove end indent

[caripizza]

Description

Pr #3001 refactored tree-item to match latest Figma designs. In doing so, I repurposed a --calcite-tree-padding-y CSS var for the item's margin-inline styles as well. However, it came up recently with the Dashboards team that they'd like to fine-tune the top/bottom item spacing independently of the left/right spacing. cc @ellenupp

This issue should:

• refactor tree-item to derive it's margin-inline styles from the TW config instead of the padding-y var, so consumers can set the padding-y CSS var value to something different without affecting the left/right margins on a tree-item.
• remove the margin-inline-end style from the children-container's tree-items.

Acceptance Criteria

a ) Updating the --calcite-tree-padding-y CSS var value on calcite-tree-item only changes its top/bottom spacing
b) There are no more margin-inline-end styles (end-indentation) on tree-items

Relevant Info

n/a

Which Component

calcite-tree-item

Example Use Case

See issues #2210 and #3127 for more details on the related designs driving this request.

[caripizza]

@benelan and @jcfranco - can we add this one to the current sprint?

[benelan]

sure thing!

[github-actions]

Installed and assigned for verification.

[benelan]

@macandcheese can you please help me verify this installed design issue?

[macandcheese]

LGTM although I don't believe that css variable should be customizable, teams can just adjust padding themselves with divs they slot. Oh well, it's fine for now and we can re-visit when these get refactored with the list-item slot paradigm.