Change `createLocalizableString` API

[RomanTsukanov]

This is what a call of the createLocalizableString looks like:

this.createLocalizableString("caption", this, true, "descriptiveTextCaption");

3 out of 4 parameters cannot be understood at a glance, without being looked up in the docs.

Suggested API:

this.createLocalizableString({
  name: "caption",
  owner: this,
  supportsMarkdown: true,
  dictionaryKey: "descriptiveTextCaption" // <-- clarify why this parameter can be boolean
});