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.

cmd/geth/usage.go

@@ -207,6 +207,8 @@ var AppHelpFlagGroups = []flagGroup{
 		Name: "VIRTUAL MACHINE",
 		Flags: []cli.Flag{
 			utils.VMEnableDebugFlag,
+			utils.EVMInterpreterFlag,
+			utils.EWASMInterpreterFlag,
 		},
 	},
 	{