Tool window doesn't get focused when opened

[alirezamirian]

Reproduction scenario:

1. Within the left side, have two tool windows; one at the top (primary) and one at the bottom (secondary).
2. Open the secondary, leaving the primary closed.
3. Open the primary.
   The focus should be moved to the primary tool window when it opens, but it will remain in the secondary.

Problem

The focus doesn't actually "remain" within the secondary tool window. The secondary tool window is remounted as the primary window is mounted. Both will attempt to autofocus on mount and the second one wins, simply because it's rendered after the primary one.

Explanation

In SideDockedState, primary and secondary tool windows are normalized into a main and split view. When only the secondary window is opened, it will take up the main slot. When both windows are open, the secondary window will take up the split slot. So the secondary window will be re-mounted because it's moved across react tree.

Potential solution

Always render the primary and secondary windows in the same place in react tree. Render null if one is empty. There may be a need for change in ThreeViewSplitter, in case it doesn't properly support only passing lastView.

Test case

jui/packages/jui/src/ToolWindowsImpl/DefaultToolWindows.cy.tsx

Lines 163 to 189 in f38065c

	it("opens and focuses tool window (in the same anchor) if currently closed", () => {
	cy.mount(
	<ThemeProvider theme={new Theme(darculaThemeJson as any)}>
	<WithActivateToolWindowKeymap
	initialState={{
	"First window": toolWindowState({ anchor: "left" }),
	"Second window": toolWindowState({
	anchor: "left",
	isSplit: true,
	isVisible: true,
	}),
	}}
	/>
	</ThemeProvider>
	);
	cy.realPress(["Meta", "1"]);
	cy.findByTestId("First window").should("exist");
	/**
	* Known issue: https://github.com/alirezamirian/jui/issues/42
	* Inverted assertion, in the absence of it.fail(). Just to make sure it will not be overlooked when the issue
	* is resolved. The assertion should be `.should("have.focus")`.
	*/
	cy.findByTestId("First window")
	.find("input")
	.eq(0)
	.should("not.have.focus");
	});