LibWasm: Start implementing a naive bytecode interpreter

As the parser now flattens out the instructions and inserts synthetic
nesting/structured instructions where needed, we can treat the whole
thing as a simple parsed bytecode stream.
This currently knows how to execute the following instructions:
- unreachable
- nop
- local.get
- local.set
- {i,f}{32,64}.const
- block
- loop
- if/else
- branch / branch_if
- i32_add
- i32_and/or/xor
- i32_ne

This also extends the 'wasm' utility to optionally execute the first
function in the module with optionally user-supplied arguments.

Userland/Libraries/LibWasm/Printer/Printer.cpp

@@ -14,7 +14,7 @@ struct Names {
     static HashMap<OpCode, String> instruction_names;
 };
 
-static String instruction_name(const OpCode& opcode)
+String instruction_name(const OpCode& opcode)
 {
     return Names::instruction_names.get(opcode).value_or("<unknown>");
 }