Add transient storage slot support in StorageSlot.sol (#4980)

Co-authored-by: ernestognw <ernestognw@gmail.com>

test/helpers/strings.js

@@ -0,0 +1,5 @@
+module.exports = {
+  // Capitalize the first char of a string
+  // Example: capitalize('uint256') → 'Uint256'
+  capitalize: str => str.charAt(0).toUpperCase() + str.slice(1),
+};