[Bug]: There's seemingly no way to get a template declaration's type parameters defaults as Type instances

[TomerAberbach]

Describe the bug

Given a TemplatedType that passes isTemplateDeclaration, there doesn't seem to be a way to get the defaults of its type parameters as Type instances.

This blocks some of what I want to implement in TomerAberbach/typespec-fast-check#76. I want to emit functions with default values for each templated type. e.g.

model TemplateModel<A, B = string> {
  a: A,
  b: B
}

Should become the following from my emitter:

import * as fc from "fast-check";

export const TemplateModel = (a, b = fc.string()) =>
  fc.record({
    a: a,
    b: b,
  });

But I can't figure out any way to get the Type for the = string default from the TypeSpec file.

Reproduction

See above.

Checklist

• Follow our Code of Conduct
• Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion.
• The provided reproduction is a minimal reproducible example of the bug.