fix(tree): add translatable strings for selected/unselected node (#1575)

## PR Checklist

Please check if your PR fulfills the following requirements:

- [ ] Tests for the changes have been added (for bug fixes / features)
- [ ] Docs have been added / updated (for bug fixes / features)
- [ ] If applicable, have a visual design approval

## PR Type

What kind of change does this PR introduce?

<!-- Please check the one that applies to this PR using "x". -->

- [x] Bugfix
- [ ] Feature
- [ ] Code style update (formatting, local variables)
- [ ] Refactoring (no functional changes, no api changes)
- [ ] Build related changes
- [ ] CI related changes
- [ ] Documentation content changes
- [ ] Other... Please describe:

## What is the current behavior?

<!-- Please describe the current behavior that you are modifying, or
link to a relevant issue. -->

Issue Number: CDE-2311

## What is the new behavior?
Easier translation of "selected" and "unselected" strings in tree node

## Does this PR introduce a breaking change?

- [ ] Yes
- [x] No

<!-- If this PR contains a breaking change, please describe the impact
and migration path for existing applications below. -->

## Other information

---------

Co-authored-by: Valentin Mladenov <[email protected]>

projects/angular/clarity.api.md

@@ -1017,6 +1017,8 @@ export interface ClrCommonStrings {
     select: string;
     selectAll: string;
     selectedRows: string;
+    // (undocumented)
+    selectedTreeNode: string;
     show: string;
     showColumns: string;
     showColumnsMenuDescription: string;
@@ -1043,6 +1045,8 @@ export interface ClrCommonStrings {
     totalPages: string;
     unknown: string;
     // (undocumented)
+    unselectedTreeNode: string;
+    // (undocumented)
     verticalNavToggle: string;
     warning: string;
     wizardStepError: string;

projects/angular/src/data/tree-view/tree-node.html

@@ -65,8 +65,7 @@
   <ng-template #treenodeContent>
     <ng-content></ng-content>
     <div class="clr-sr-only" *ngIf="featuresService.selectable || ariaSelected">
-      <span *ngIf="ariaSelected"> selected</span>
-      <span *ngIf="!ariaSelected"> unselected</span>
+      <span> {{ariaSelected ? commonStrings.keys.selectedTreeNode : commonStrings.keys.unselectedTreeNode}}</span>
     </div>
   </ng-template>
 </div>

projects/angular/src/utils/i18n/common-strings.default.ts

@@ -126,4 +126,8 @@ export const commonStringsDefault: ClrCommonStrings = {
   fileCount: '{COUNT} files',
   clearFile: 'Clear {FILE}',
   clearFiles: 'Clear {COUNT} files',
+
+  // Tree
+  selectedTreeNode: 'selected',
+  unselectedTreeNode: 'unselected',
 };

projects/angular/src/utils/i18n/common-strings.interface.ts

@@ -301,4 +301,8 @@ export interface ClrCommonStrings {
   fileCount: string;
   clearFile: string;
   clearFiles: string;
+
+  // Tree
+  selectedTreeNode: string;
+  unselectedTreeNode: string;
 }