Add intrinsics.is_package_imported(<string>)

core/intrinsics/intrinsics.odin

@@ -2,6 +2,9 @@
 //+ignore
 package intrinsics
 
+// Package-Related
+is_package_imported :: proc(package_name: string) -> bool ---
+
 // Types
 simd_vector :: proc($N: int, $T: typeid) -> type/#simd[N]T
 soa_struct :: proc($N: int, $T: typeid) -> type/#soa[N]T