* Fixes#26128 - signature comp for jsdoc @class.
Another issue caused by js functions tagged with jsdoc
`@constructor` not having construct signatures.
A jsdoc function type that constructs a type (`function(new: Ex)`),
has a construct signature and return value inferred as the
constructed type where as a jsdoc `@constructor` has no construct
signatures, and it's call signature has a void return type
(or undefined).
i.e:
```javascript
/** @constructor **/ function E() {};
// typeof E -> call signature: () => void
/** @param {function(new: E)} d */ function c(d) {}
// typeof d -> construct: () => E
```
--
This commit fixes this (in an inelegant way) by considering `@class` function signatures as construct signatures and synthesizing it's return value _only for signature comparison_.
There might be a slight performance hit, since the synthesized return value is not cached; but changing the `@class` function's return type in `getReturnTypeOfSignature` causes other issues.
* Update jsdoc function test to fix mistake.
