Discord-like Quick Switcher (#1588)

* Proof of Concept for Quick Switcher

* Fix crash when suggestions are empty

* QuickSwitcher: Use tab name instead of a single channel

* Rebase later

* Add missing include for <functional>

* Move QuickSwitcher related classes into own subfolder

* Refactor switcher list items

Now, items are responsible for taking the right action when selected in
the switcher list. This should allow for more focused code and
responsibilities.

* Add note about memory management

* Add option to open channel in a new tab

* Add support for using the mouse

* Spawn switcher popup in the middle of the window

Works reliably on i3 at least. Might need some additional testing on
other WMs (and especially on Windows!).

* Add some icons for switcher items

Note that the final design of the list is not final but I do plan to
incorporate these in the future.

* Set Qt::Dialog window flag on switcher popup

Prevents tiling window managers like i3 from trying to tile the window.

* Rename "SwitcherItem" to "AbstractSwitcherItem"

* Add comments about what items are inserted

* Use custom model and view

Still missing: Currently selected item is not highlighted yet. You can
move between selected items with tab and arrow keys though.

* Add helper function to convert QVariant to AbstractSwitcherItem *

* Remove useless constant

* Highlight currently selected switcher item

* Use a different method for centering QuickSwitcherPopup window

* QuickSwitcherModel: Add documentation

* Add default parameter to QuickSwitcherModel::rowCount

* QuickSwitcherPopup: Add comments

* Remove outdated TODO

* QuickSwitcherModel: Init vector with default capacity

* Remove outdated comment

* Add comment about 0 ms timeout interval

* NewTabItem: Simplify interface

* Only fetch opened splits once

This is better than the prior approach since opened splits cannot change
anyways while the switcher is open.

* Use SplitContainer to pass information instead of custom type

* Allow searching for tab titles as well

Before this commit, only channel names could be searched.

* Refactor switcher item interface to be more flexible

Also show tab name and channel name in the switcher list.

* Add documentation for AbstractSwitcherItem

* Add documentation for NewTabItem

* Add comments about {begin,end}{Insert,Remove}Rows

* Remove unused method

* Replace magic size with named constant

* Add change log entry

Co-authored-by: fourtf <tf.four@gmail.com>

src/widgets/dialogs/switcher/NewTabItem.cpp

@@ -0,0 +1,60 @@
+#include "widgets/dialogs/switcher/NewTabItem.hpp"
+
+#include "Application.hpp"
+#include "providers/twitch/TwitchIrcServer.hpp"
+#include "singletons/Fonts.hpp"
+#include "singletons/Theme.hpp"
+#include "singletons/WindowManager.hpp"
+#include "widgets/Notebook.hpp"
+#include "widgets/Window.hpp"
+#include "widgets/helper/NotebookTab.hpp"
+#include "widgets/splits/Split.hpp"
+
+namespace chatterino {
+
+NewTabItem::NewTabItem(const QString &channelName)
+    : AbstractSwitcherItem(QIcon(":/switcher/plus.svg"))
+    , channelName_(channelName)
+    , text_(QString(TEXT_FORMAT).arg(channelName))
+{
+}
+
+void NewTabItem::action()
+{
+    auto &nb = getApp()->windows->getMainWindow().getNotebook();
+    SplitContainer *container = nb.addPage(true);
+
+    Split *split = new Split(container);
+    split->setChannel(
+        getApp()->twitch.server->getOrAddChannel(this->channelName_));
+    container->appendSplit(split);
+}
+
+void NewTabItem::paint(QPainter *painter, const QRect &rect) const
+{
+    painter->save();
+
+    painter->setRenderHint(QPainter::Antialiasing, true);
+
+    // TODO(leon): Right pen/brush/font settings?
+    painter->setPen(getApp()->themes->splits.header.text);
+    painter->setBrush(Qt::SolidPattern);
+    painter->setFont(getApp()->fonts->getFont(FontStyle::UiMediumBold, 1.0));
+
+    QRect iconRect(rect.topLeft(), ICON_SIZE);
+    this->icon_.paint(painter, iconRect, Qt::AlignLeft | Qt::AlignVCenter);
+
+    QRect textRect =
+        QRect(iconRect.topRight(),
+              QSize(rect.width() - iconRect.width(), iconRect.height()));
+    painter->drawText(textRect, Qt::AlignLeft | Qt::AlignVCenter, this->text_);
+
+    painter->restore();
+}
+
+QSize NewTabItem::sizeHint(const QRect &rect) const
+{
+    return QSize(rect.width(), ICON_SIZE.height());
+}
+
+}  // namespace chatterino