core/vm: add switches to select evm+ewasm interpreters (#17687)

Interpreter initialization is left to the PRs implementing them.
Options for external interpreters are passed after a colon in the
`--vm.ewasm` and `--vm.evm` switches.

core/vm/interpreter.go

@@ -39,6 +39,11 @@ type Config struct {
 	// may be left uninitialised and will be set to the default
 	// table.
 	JumpTable [256]operation
+
+	// Type of the EWASM interpreter
+	EWASMInterpreter string
+	// Type of the EVM interpreter
+	EVMInterpreter string
 }
 
 // Interpreter is used to run Ethereum based contracts and will utilise the