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>

runtime.go

@@ -22,7 +22,7 @@ import (
 //
 //	module, _ := r.InstantiateModuleFromBinary(ctx, wasm)
 type Runtime interface {
-	// NewModuleBuilder lets you create modules out of functions defined in Go.
+	// NewHostModuleBuilder lets you create modules out of functions defined in Go.
 	//
 	// Ex. Below defines and instantiates a module named "env" with one function:
 	//
@@ -30,8 +30,8 @@ type Runtime interface {
 	//	hello := func() {
 	//		fmt.Fprintln(stdout, "hello!")
 	//	}
-	//	_, err := r.NewModuleBuilder("env").ExportFunction("hello", hello).Instantiate(ctx, r)
-	NewModuleBuilder(moduleName string) ModuleBuilder
+	//	_, err := r.NewHostModuleBuilder("env").ExportFunction("hello", hello).Instantiate(ctx, r)
+	NewHostModuleBuilder(moduleName string) HostModuleBuilder
 
 	// CompileModule decodes the WebAssembly binary (%.wasm) or errs if invalid.
 	// Any pre-compilation done after decoding wasm is dependent on RuntimeConfig or CompileConfig.