Support for GL_EXT_ray_tracing

[Cyphall]

Is your feature request related to a problem? Please describe.
Currently, when editing a raytracing shader, some raytracing-specific keywords such as rayPayloadEXT and hitAttributeEXT are unknown to this plugin, which means they are wrongly marked as errors.

Describe the solution you'd like
A support for this extension (even basic, like just registering the keywords to make the parser happy) would be great.

[jstefanelli]

Also would like to see this. I would try to implement this myself, but I don't know how (or where even) to modify the lexer to add the required qualifiers and keywords