…opups

Additional changes:
- Added a 'Pin' button to the floating popup's toolbar. When a tool is pinned, the popup will not close automatically after the action is executed.
- Added a virtual function to the `ViewHexEditor::Popup` class, allowing implementations to specify a tool window title.

Before this change, the modifications to the tool popup UIs did not respect the user's scaling factor settings.

…dd missing EndPopup

…title texts

…-focused

…de to ViewHexEditor::drawPopup()

…window when the user isn't hovering over it

In the previous approach, I was using ImGuiWindowFlags_NoBackground combined with an explicitly drawn background rectangle to correctly set the window transparency within ImGuiExt::Begin/EndHoveringPopup(). However with this approach, there was a small but noticeable gap between the window's external borders and the background rectangle, due to the configured default padding.

With this new approach, the decision to apply the transparency will always be delayed by one frame, but theis way the whole window can be set to being transparent before ImGuiExt::BeginHoveringPopup().

…e user isn't hovering over

…ect until the user hovers over it

…d PopupWindowAlpha value

This fix restores the previously decided behavior ensuring that newly opened popup windows are initially non-transparent, until the user hovers over them for the first time.

…isappear on click

This if branch handles the case when the user clicks outside of the currently visible popup, and it loses focus. But if the popup loses focus while `ImGui::IsWindowHovered()` still returns true, it means that the focus loss was not caused by the user clicking away, so it should not be closed yet. Since the focus loss was only registered when clicking on the background / title bar of the popup, and not any of its child widgets, this could be an ImGui bug.

…ly multiplying with the scale factor