Summary:
This patch moves the "Open", "Open With", and "Open in" items to the top of the context menu to reap the following benefits:
- Move the "Open" and "Open With" items closer to the top since they're commonly used items, and right now they're buried in the middle of the menu
- Group related functionality
- Consistency with other common platforms (macOS Finder and Windows Explorer both have these items at the top of the context menu)

For folders, the "Open With" entries are moved higher, but not all the way to the top, since the "open in New tab/folder" entries are more useful.

Test Plan:
Tested all menu items in the context menu for files, folders, and links; all still work.

Context menu for single file:
{F5806809}

Context menu for multiple files:
{F5806810}

Context menu for single folder:
{F5806811}

Context menu for multiple folders:
{F5806812}

Context menu for symlink to folder:
{F5806815}

Reviewers: #dolphin, #vdg, elvisangelaccio, abetts

Reviewed By: #dolphin, #vdg, elvisangelaccio, abetts

Subscribers: markg, abetts, elvisangelaccio

Differential Revision: https://phabricator.kde.org/D11884