[AutoDiff] Fix `@differentiable(linear)` type parsing ambiguity. (#27646)
Handle the case where `@differentiable(linear)` is followed by a type alias or another type attribute.
```swift
typealias linear = (Float) -> Float
let property: @differentiable(linear) linear // okay
let property: @differentiable(linear) @convention(c) linear // okay
```
Resolves [TF-576](https://bugs.swift.org/browse/TF-576).