fix(build): enable loose (lighter) Babel syntax compilation

for some safe syntax transforms, assuming public class fields do not
shadow an existing getter in current class / subclass or superclass.
Can also be achieved with the setPublicClassFields compiler assumption.

See:
- https://babeljs.io/docs/en/assumptions#setpublicclassfields
- https://babeljs.io/docs/en/babel-plugin-proposal-class-properties#loose

web3.js/babel.config.json

@@ -9,6 +9,23 @@
     ["@babel/preset-typescript"]
   ],
   "plugins": [
-    "@babel/plugin-proposal-class-properties"
+    [
+      "@babel/plugin-proposal-class-properties",
+      {
+        "loose": true
+      }
+    ],
+    [
+      "@babel/plugin-proposal-private-methods",
+      {
+        "loose": true
+      }
+    ],
+    [
+      "@babel/plugin-proposal-private-property-in-object",
+      {
+        "loose": true
+      }
+    ]
   ]
 }