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.

eth/config.go

@@ -121,6 +121,11 @@ type Config struct {
 
 	// Miscellaneous options
 	DocRoot string `toml:"-"`
+
+	// Type of the EWASM interpreter ("" for detault)
+	EWASMInterpreter string
+	// Type of the EVM interpreter ("" for default)
+	EVMInterpreter string
 }
 
 type configMarshaling struct {