feat: load shader parameter values from .cfg preset files

[DrFlarp]

Addresses #685

Minarch will now check for any shader parameters when loading a .cfg preset.

Use cases include:

• user wants to have multiple sets of default settings for a shader, for example, different cores
• shader dev wants to go back-and-forth between two configurations

(edit: btw, changes are fully orthogonal to my other shader-related PR)