Allow dumping of generated shaders for later inspection

While trying to understand lackluster performance of cluster demo running on q3viewer on embedded platforms (especially on Renesas R-Car M3 Draak) it turned out that dumping shaders needed hacking. e0150566 helped to dump whole bunch of shaders (9 vertex and 9 fragment) from desktop version and while studying some of them, there seemed to be varyings that are calculated on vertex shader and passed to fragment shader, where they are not used in the end.

Trying to backtrace, how those shaders came to be in such a way is pretty difficult as the generated shaders don't have any obvious clues (for non initiated person) what path the generation took in the source code.

Thus, I suggest that 1) the dumping of shaders should be inbuilt and easy to activate. For example for all the layers or just selected ones. 2) While the shaders are generated, there should be some trace (tags, variables, functionnames), what went into the generation process. Perhaps these traces could be inserted only when the intention is to dump the generated shaders.

In summary, to improve the shaders and removing redundant generated code, it should be possible to dump the selected shaders easily and the dumped shaders should have information to help traceback in the shader generators, to fix found issues.