Support for variadic functions in documentation popup.

Summary:
This shows the documentation for functions defined as

```
function foo(...$params) {}
function foo(A ...$params) {}
```

in the form of

```
void foo ([mixed ...params])
void foo ([A ...params])
```

In the first case, $params itself is shown as

```
array params
```

and in the latter as

```
array of (A) params
```

Reviewers: zhigalin

Reviewed By: zhigalin

Subscribers: aacid, zhigalin, kdevelop-devel

Differential Revision: https://phabricator.kde.org/D6256