[TabView] Fix issue where hitting Ctrl+F4 would not resize tabs

[marcelwgn]

Description

Fixed this by updating call to UpdateTabWidths on RequestCloseTab.

Motivation and Context

Closes #4971

How Has This Been Tested?

Added new interaction test

Screenshots (if appropriate):

[beervoley]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[zadjii-msft]

🤔

@beervoley @chingucoding Did this PR only fix this for specifically the built-in ctrl+f4 shortcut? Over in the Terminal, we're closing tabs with tabView.TabItems().RemoveAt

https://github.com/microsoft/terminal/blob/9662bc69102e2e152a062a9060cb63d2742582d3/src/cascadia/TerminalApp/TabManagement.cpp#L511

and that doesn't seem fixed in 2.7. See microsoft/terminal#9822. Should we get #4971 reopened, or should I file a new issue?

[beervoley]

@zadjii-msft @chingucoding looks like we're not always calling UpdateTabWidths() in the scenario of underlying tab collection change.

microsoft-ui-xaml/dev/TabView/TabView.cpp

Lines 683 to 689 in 51cf944

	if (TabWidthMode() == winrt::TabViewWidthMode::Equal)
	{
	m_updateTabWidthOnPointerLeave = true;
	if (args.Index() == TabItems().Size())
	{
	UpdateTabWidths(true, false);
	}

If the Tab was deleted manually, we only call UpdateTabWidths() if the last Tab was removed. I can't remember why we did it this way :(
@chingucoding would you like to submit a fix for this? should be pretty straightforward:)

[marcelwgn]

Sure thing, I'll take a look at this @beervoley and @zadjii-msft !