all: refactor reflect package

This is a big commit that changes the way runtime type information is stored in
the binary. Instead of compressing it and storing it in a number of sidetables,
it is stored similar to how the Go compiler toolchain stores it (but still more
compactly).

This has a number of advantages:

  * It is much easier to add new features to reflect support. They can simply
    be added to these structs without requiring massive changes (especially in
    the reflect lowering pass).
  * It removes the reflect lowering pass, which was a large amount of hard to
    understand and debug code.
  * The reflect lowering pass also required merging all LLVM IR into one
    module, which is terrible for performance especially when compiling large
    amounts of code. See issue 2870 for details.
  * It is (probably!) easier to reason about for the compiler.

The downside is that it increases code size a bit, especially when reflect is
involved. I hope to fix some of that in later patches.

src/runtime/hashmap.go

@@ -506,7 +506,7 @@ func hashmapFloat64Hash(ptr unsafe.Pointer, seed uintptr) uint32 {
 
 func hashmapInterfaceHash(itf interface{}, seed uintptr) uint32 {
 	x := reflect.ValueOf(itf)
-	if x.RawType() == 0 {
+	if x.RawType() == nil {
 		return 0 // nil interface
 	}