Special-case JSDocVariadicType in JSDocSignature

[sandersn]

Currently in Corsa, ...T is always interpreted as T[], which is considerably
simpler than in Strada. However, there is no
way to express rest parameters in a @callback or @overload tag. This
PR special-cases ... in @param tags in JSDocSignature, which is how these tags parse,
such that instead of ...T --> T[],
it reparses as ...T --> ...paramName: T.

Notes:

1. This is how it used in unifier, which is a heavily jsdoc'ed
   codebase checked with Strada.
2. This PR removes the variadic type in reparsing, meaning that the
   author needs to provide an array type, like ...[number, number] for
   example. This is still a subset of the Strada semantics.
3. Code that relies on Strada treating ... both as rest and as
   array type in this position gets an error that an array type is
   required. This should help other uses update to Corsa semantics.

The new semantics are inconsistent but they are still fairly simple and
should match with how people use ...T in Strada. See how the new test
based on example code from unifiedjs uses ...T to mean rest parameter
on @overload and to mean T[] on a @param of the implementation.

[Copilot]

Pull Request Overview

This PR implements special handling for JSDoc variadic types (...T) in JSDoc signatures (used in @callback and @overload tags). Instead of always converting ...T to T[], the change enables rest parameter syntax (...paramName: T) when variadic types appear in JSDoc signatures, while maintaining the array conversion behavior in other contexts.

Key changes:

• Modified JSDoc signature reparsing to detect variadic types and convert them to rest parameters
• Added test coverage for @overload scenarios with variadic parameters
• Updated baseline expectations to reflect the new rest parameter semantics

Reviewed Changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

File	Description
testdata/tests/cases/conformance/jsdoc/jsdocVariadicInOverload.ts	New test case demonstrating variadic types in @overload tags, based on unifiedjs code
testdata/baselines/reference/submodule*/callbackTagVariadicType.*	Updated baselines showing variadic types now generate rest parameters with different error messages
testdata/baselines/reference/conformance/jsdocVariadicInOverload.*	New baseline files showing expected output for the new test case
internal/parser/reparser.go	Core implementation detecting JSDocVariadicType and converting to rest parameter syntax

Comments suppressed due to low confidence (1)

testdata/tests/cases/conformance/jsdoc/jsdocVariadicInOverload.ts:47

• The test uses undefined variables 'x', 'y', 'z' which will cause TypeScript errors unrelated to the feature being tested. Consider defining these variables with appropriate types or using literal values to focus the test on variadic parameter behavior.

p.use(x, y, z);

[sandersn]

this shows the old, still unsupported semantics where the parameter args becomes a rest parameter and the type string becomes string[]. Only the first happens now, based on seeing how a real person (Titus Woormer) wrote overloads.