Release 12.2.0

Changes in this release:

• Support GLSL_EXT_shader_tile_image
• Support GL_EXT_ray_tracing_position_fetch
• Support custom include callbacks via the C API
• Add preamble-text command-line option
• Accept variables as parameters of spirv_decorate_id
• Fix generation of conditionals with a struct result
• Fix double expansion of macros
• Fix DebugCompilationUnit scope
• Improve line information