* update documentation
   - move `@shuffle` to be sorted alphabetically
   - remove mention of LLVM
   - minor clarifications & rewording
 * introduce ir_resolve_vector_elem_type to avoid duplicate compile
   error message and duplicate vector element checking logic
 * rework ir_analyze_shuffle_vector to solve various issues
 * improve `@shuffle` to allow implicit cast of arrays
 * the shuffle tests weren't being run