pybricksMicropython/lib: replace parser

This replaces the Python parsing library. The python-ast package has
really poor performance (many seconds to parse a 500 line file). The
new package can parse a file about 100 times faster.

config/webpack.config.js

@@ -802,5 +802,6 @@ module.exports = function (webpackEnv) {
     // Turn off performance processing because we utilize
     // our own hints via the FileSizeReporter
     performance: false,
+    ignoreWarnings: [/Failed to parse source map/],
   };
 };