Consolidate Ender-3 V2 DWIN common code

[thinkyhead]

• Move common functions for the Ender-3 V2 DWIN screens to a common folder.
• Adjust API to avoid naming conflict with DWIN_String class.
• Use ui.buzzer_enabled flag instead of a custom flag for JyersUI.
• Use Z_VALUES_ARR to get the mesh points for JyersUI.
• Allow brightness adjustment for all E3V2 with M256.
• Make LockScreenClass a static singleton.
• Apply standard file headings, author note below. Not suitable for LGPL.

The JyersUI code referred to nonexistent mesh_conf.mesh_z_values for PROBE_MANUALLY so that needs review.