Use the more appropriate "two sliders" icon for "configure"

Summary:
Right now, the Breeze icon for "Configure" is sub-optimal and nondescript, and has little visual connection to the idea of "configure me! Settings over here!"

There is already a better icon: a "two sliders" symbol that's currently used for configuring shortcuts, for some odd reason. Plasma deliberately uses this "two sliders" icon instead of the default one in many places (e.g. KRunner) and System Settings already uses "two sliders" iconography in its own icon. Also, the Breeze icon theme uses this icon for "configure" in GTK apps. It's very much a more appropriate icon.

This patch uses the superior "two sliders" icon for "configure" in all contexts, and adjusts symlinks to maintain compatibility for places where the existing icon should be used.

Also, the "configure shortcuts" icon changes to one that looks like a keyboard, which seems more appropriate given the feature itself.

Test Plan:
Deploy change, switch to Breeze Dark and then back to Breeze light again

Better icons in settings menu:

Better icon in the open/save dialog:

Better icons in Window Decorations KCM:

No change for Properties menu items:

No change for KRunner (it was already using the "two-sliders" icon):

No change for Preferences in GTK apps (they were already using the "two-sliders" icon):

Also tested with Breeze dark. Same consistent results.

Reviewers: VDG, Plasma, Breeze, abetts

Reviewed By: VDG, abetts

Subscribers: hein, bruns, abetts, sharvey, Frameworks

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D12034