Set Tab tooltip explicitly (microsoft#8298)

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## Summary of the Pull Request
The tab tooltip is no longer empty when it was toggle zoomed.
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## References

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## PR Checklist
* [x] Closes microsoft#8199 
* [ ] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [ ] Tests added/passed
* [ ] Documentation updated. If checked, please file a pull request on [our docs repo](https://github.com/MicrosoftDocs/terminal) and link it here: #xxx
* [ ] Schema updated.
* [ ] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

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## Detailed Description of the Pull Request / Additional comments

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## Validation Steps Performed

src/cascadia/TerminalApp/TerminalTab.cpp

@@ -50,7 +50,6 @@ namespace winrt::TerminalApp::implementation
                 tab->SetTabText(title);
             }
         });
-
         // Use our header control as the TabViewItem's header
         TabViewItem().Header(_headerControl);
     }
@@ -76,6 +75,13 @@ namespace winrt::TerminalApp::implementation
         _RecalculateAndApplyTabColor();
     }
 
+    void TerminalTab::_SetToolTip(const winrt::hstring& tabTitle)
+    {
+        WUX::Controls::ToolTip toolTip{};
+        toolTip.Content(winrt::box_value(tabTitle));
+        WUX::Controls::ToolTipService::SetToolTip(TabViewItem(), toolTip);
+    }
+
     // Method Description:
     // - Returns nullptr if no children of this tab were the last control to be
     //   focused, or the TermControl that _was_ the last control to be focused (if
@@ -265,6 +271,7 @@ namespace winrt::TerminalApp::implementation
 
             // Update the control to reflect the changed title
             _headerControl.Title(activeTitle);
+            _SetToolTip(activeTitle);
         }
     }
 

src/cascadia/TerminalApp/TerminalTab.h

@@ -98,6 +98,8 @@ namespace winrt::TerminalApp::implementation
 
         void _MakeTabViewItem();
 
+        void _SetToolTip(const winrt::hstring& tabTitle);
+
         void _CreateContextMenu() override;
 
         void _RefreshVisualState();