Implement a solution for regenerating content of dynamic resources when the context is lost

[mvaligursky]

When a webgl context is lost, dynamically generated resources are invalidated and their content is lost. Examples:

• content of render target textures (this includes runtime lightmaps, area light LUTs, one time rendered shadow maps ..)
• content of dynamically generated VBs and IBs (instanced geometry VB, many others)

Ideally we should have a solution allowing this to be handled - either by the engine internally if possible (if a cpu storage of the data exists, which it does for VB/IB), or by exposing some events for the user to regenerate their data.

[mvaligursky]

I just checked .. we already have events on the device, which allow the user to handle the resources they generate - they can re-render their render targets and similar.

            this.fire('devicelost');
            this.fire('devicerestored');

What is left to do is to automatically handle the resources the engine owns:

• re-render one time shadow maps - [Fix] Re-render all shadows when the device context is restored #7757
• re-render clustered cookies - [Fix] Re-render cookie atlas use by clastered lighting when the device context is restored #7758
• regenerate env-atlas from cubemaps possibly
• maybe others

[mvaligursky]

related forum post: https://forum.playcanvas.com/t/lightmap-will-lose-shadow-data-when-bake-it-again/37883