Support for referencing Objects in T helper

[MarkLunney]

It would be convenient to be define strings values in an Object and be able to reference the values using the T helper:

const Pets = {
  cat: "Cat",
  dog: "Dog",
};

return T(Pets.cat)

This currently throws the following error:

yarn extract-strings --outfile=./src/i18n/en/strings.json "src/**/!(*.test|*.d).{ts,tsx}"
yarn run v1.22.19
Extracting strings from '[redacted]' + 1597 other files...
undefined:3
return Pets.cat
^

ReferenceError: Pets is not defined
    at eval (eval at evaluate ([redacted]/node_modules/t-i18n/scripts/extract-strings.js:21:22), <anonymous>:3:1)

The following doesn't produce the same error:

const cat = "Cat";

return T(cat)