Require documentation of unions

[tjprescott]

Closes #516 .

This PR:

• Exempts discriminator unions from requiring documentation
• Requires documentation of the union itself
• Requires documentation of named union variants, but not symbolic variants

REST API Specs
Violations: 27
Azure/azure-rest-api-specs#28849

[azure-sdk]

All changed packages have been documented.

• ✅ @azure-tools/typespec-azure-core

Show changes

@azure-tools/typespec-azure-core - fix ✏️

Require documentation on most unions.

[azure-sdk]

You can try these changes at https://cadlplayground.z22.web.core.windows.net/typespec-azure/prs/740/

Check the website changes at https://tspwebsitepr.z22.web.core.windows.net/typespec-azure/prs/740/

[tjprescott]

For reviewers, this currently is the minimal passing behavior:

/** Describes the kind of Pet. */
union PetStyle1 {
  /** Kitty */
  Cat: "cat",
  /** Doggy */
  Dog: "dog",
  string
}

/** Describes the kind of Pet */
union PetStyle2 {
  "cat",
  "dog",
  string
}

The logic only requires documentation for named variants. string doesn't require it because it's just a symbol, and any documentation added is ignored by the Autorest emitter anyhow. However, in the second style, the emitter basically converts this to the same Swagger as the first, so should documentation be required here as well?

Updated the logic to require documentation even on string literal variants.