WASM: NFC. Rename WasmPrimitive into WasmAutoboxed and add few comments.

libraries/stdlib/wasm/internal/kotlin/wasm/internal/WasmAnnotations.kt

@@ -32,9 +32,11 @@ internal annotation class WasmArrayOf(
 @Retention(AnnotationRetention.BINARY)
 internal annotation class WasmReinterpret
 
+// This tells backend to insert box/unbox intrinsics around the annotated class. It's used to represent built-in types without making them
+// explicitly "inline" (or "value" in the newest terminology).
 @Target(AnnotationTarget.CLASS)
 @Retention(AnnotationRetention.BINARY)
-internal annotation class WasmPrimitive
+internal annotation class WasmAutoboxed
 
 /**
  *  Replace calls to this functions with specified Wasm instruction.