Enhancement: [calcite-tree] add selection-mode "none"

[caripizza]

Description

Support a calcite-tree selection-mode of "none", for displaying a hierarchical list of tree-items which display no icons on hover/focus, and do not allow any items to be selected.

Acceptance Criteria

A new selection-mode of "none" is added to the TreeSelectionMode type values. When a tree has selection-mode "none", no child tree-items can be selected, and no icons appear on :hover or :focus.

Relevant Info

Related issue tied to this request: #2210 (cc @bpatterson88)

Which Component

calcite-tree, calcite-tree-item

Example Use Case

(See screenshots provided in #2210)

[caripizza]

Here's one example I found in the wild of "none" selection-mode with IntegralUI's TreeView component for Angular:
https://www.lidorsystems.com/support/articles/angular/treeview/treeview-multi-select.aspx

[macandcheese]

This implementation from SAP also uses "none": https://sap.github.io/ui5-webcomponents/playground/components/Tree/

[ellenupp]

Use case for Dashboards:
We are using a tree to represent the layout of the elements in the dashboard. The tree does not need a selection state. Clicking a tree item should place focus on that item but not otherwise change its state. Tree items don't need bullet point and instead child items have a custom icon.

[jcfranco]

Please add your planning poker estimate with ZenHub @caripizza

[paulcpederson]

We also have a use case for this. Seems pretty straight forward, I could try to add this?

[benelan]

Sure, @paulcpederson, we always appreciate your help!

[jcfranco]

Stealing this one... 👿

[github-actions]

Installed and assigned for verification.

[geospatialem]

Verified in beta.92 👍🏻