Refactor ShaderEditorPlugin to use ScriptEditor

[TheDying0fLight]

• Resolves Refactor code editors #28607
• Related Refactor TextEditor and ScriptTextEditor #114917

Changes

• re-implements ShaderEditorPlugin using the ScriptEditor class used for the ScriptEditorPlugin
• ShaderEditor classes inherit from ScriptEditorBase classes
• indirectly adds some script editor features, for example a tab history or function folding
• some shortcuts are changed to only work when a ScriptEditor is focused, because of ScriptEditor focus loss when using next_script / prev_script shortcuts #117209 these sometimes stop working until an editor is focused again by clicking on it

Changes that could be controversial

• VisualShaderEditor now has a menu bar at the top reducing space. I did not find a nice way around this. If it stays this way the menu bar could be used for the toggle_files_panel_button so it is at the same location for each editor type.
• I created a shared build function for the context and file menus as they have several options in common. This makes sure the order for the same options are the same in the two menus and therefore rearranges some of them.
• I tried to make the Shader Editor (file and context) menus more similar to the Script Editor menus for more consistency between the editors and the Shader Editor menus have a lot more options now.

[AThousandShips]

Code looks good to me! Great work!

Haven't tested the functionality