feat: Add quick tabs controls to toolbar

[ok-developer]

Description

Added quick actions for tabs manipulation: add new, list existed and close current. Same as in Notepad++.

Technical Details

• Uses all existed actions: MainWindow::newFile(), MainWindow::closeCurrentFile() and tabs listing nearly same workflow from CDockAreaTitleBar::onTabsMenuAboutToShow();
• Buttons visibility options for future customization(if else);
• 3 extra icons added from Lucide community;
• Tabs listing button disabled in DockManager via config flag.

[dail8859]

Hi @ok-developer! Thanks for this PR.

Personally, I've never been a fan of having these options in Notepad++ since there's other ways to do most of this behavior, however I know many other people find it useful, and this code really just reuses mostly existing logic and keeps everything self-contained. Plus it can be configurable later.

So my first few initial asks are:

1. Remove the use of TabsQuickActionsBar::Private as nothing else in the code base uses a private struct since there's no intention to expose these classes externally and needing to keep a stable ABI.
2. I'd just ask to try to keep the formatting similar to the existing code. This mostly a failure on my part as I have no clear guidance or tools to enforce a particular style, but for now just use the existing code and keep it fairly similar.
3. Also, I think for any active editors I'd request making the QAction text bold rather than just pretending it with "> " so that it is more visual distinct.

But overall I think the implementation makes sense keeping nearly everything to that single TabsQuickActionsBar and the icons are clean and simple.

The other thing I always wrestle with is where to put the 'glue' logic. Right now, the MainWindow knows about TabsQuickActionsBar implementation but in theory the main window could be passed into the TabsQuickActionsBar constructor and let that do all the connecting...I'm fine with the current implementation though...just a thought.

[ok-developer]

@dail8859, You're right: it's a small improvement, but the layout of these buttons is already stuck in muscle memory. The first time, I was even a bit confused when I didn't find them)

Updated.

[dail8859]

Overall looks good. I cleaned it up a bit but kept all the functionality.

Thanks for the PR!