[api] Fix crash accessing tuple type reference data

[Andrew Branch (andrewbranch)]

Fixes #63869
Fixes #64065
Closes #64066

The client-side API now has

t.isTypeReference();   // true, let's say
t.isTupleTypeTarget(); // false, let's say

if (t.isTupleType()) {
  t;                            // TupleTypeReference
  const target = t.getTarget(); // TupleType
  target.fixedLength;           // boolean

  target.isTupleTypeTarget();    // true
  target.isTupleType();          // true
  target.getTarget() === target; // true
}

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[Anders Hejlsberg (ahejlsberg)]

Hmm, seems like isTupleType now means different things between the function by that name in the checker and the exposed API function. From the checker's point of view, isTupleType returns true if the given type is a type reference to a synthesized tuple base class (which will have ObjectFlagsTuple set). But, if I'm not mistaken, that's what isTupleTypeReference in the API now does. And I'm not quite sure what the API's isTupleType does?

[Anders Hejlsberg (ahejlsberg)]

I should add here that a synthesized tuple base class instance also serves as a type reference to itself. So, the synthesized tuple base class has both ObjectFlagsTuple and ObjectFlagsReference set. This is the same pattern as regular class and interface types.

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Pull request overview

Copilot reviewed 11 out of 11 changed files in this pull request and generated no new comments.

[Jake Bailey (jakebailey)]

LGTM if this is what Anders was saying made sense