Renames ModuleBuilder to HostModuleBuilder and drops memory and globals (#812)

We at one point considered making `ModuleBuilder` create complete
WebAssembly binaries. However, we recently spun out
[wabin](https://github.com/tetratelabs/wabin), which allows this.

Meanwhile, the features in `ModuleBuilder` were confusing and misused.
For example, the only two cases memory was exported on GitHub were done
by accident. This is because host functions act on the guest's memory,
not their own.

Hence, this removes memory and globals from host side definitions, and
renames the type to HostModuleBuilder to clarify this is not ever going
to be used to construct normal Wasm binaries.

Most importantly, this simplifies the API and reduces a lot of code. It
is important to make changes like this, particularly deleting any
experimental things that didn't end up useful.

Signed-off-by: Adrian Cole <adrian@tetrate.io>
Co-authored-by: Anuraag Agrawal <anuraaga@gmail.com>

api/wasm.go

@@ -95,7 +95,7 @@ const (
 	//	(func (import "env" "f") (param externref) (result externref))
 	//
 	// This can be defined in Go as:
-	//  r.NewModuleBuilder("env").ExportFunctions(map[string]interface{}{
+	//  r.NewHostModuleBuilder("env").ExportFunctions(map[string]interface{}{
 	//    "f": func(externref uintptr) (resultExternRef uintptr) { return },
 	//  })
 	//
@@ -229,7 +229,7 @@ type FunctionDefinition interface {
 	ExportNames() []string
 
 	// GoFunc is present when the function was implemented by the embedder
-	// (ex via wazero.ModuleBuilder) instead of a wasm binary.
+	// (ex via wazero.HostModuleBuilder) instead of a wasm binary.
 	//
 	// This function can be non-deterministic or cause side effects. It also
 	// has special properties not defined in the WebAssembly Core