Update TS codegen - change getFullyQualifiedName return type from string to string literal

[rametta]

Makes the return type of static getFullyQualifiedName(): string be a string literal instead of just the string type. This helps make the return type be more specific instead of just a generic string - which helps with other tools that run static analysis on the generated code types.

Changes:

// before
static getFullyQualifiedName(): string {
  return "Some.Name";
}

// after
static getFullyQualifiedName(): "Some.Name" {
  return "Some.Name";
}

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[rametta]

Just signed the CLA, thanks!

[rametta]

@bjornharrtell sorry to tag you but I saw you on some other TS related PR's and thought you might be able to review this one too. Would be much appreciated

[bjornharrtell]

LGTM 👍

[rametta]

Any chance we could merge this one? Or do we need another approval first?