Bad construction of return type in `AutoapiSummary` leads to bad signature mangling with autodoc

Hello,

I noticed that module-level functions that were summarized with AutoapiSummary would display their return type instead of their parameters list.
I.e.:

my_function(→ Collection[MyType])

Instead of:

my_function(arg1, arg2, arg3)

This issue only affects summarized functions or methods that have a return type.

I identified this change as the problem: https://github.com/readthedocs/sphinx-autoapi/commit/72707183744ff9daabffc787f9f1ce094630e547#diff-dfb37c7639343e616e90196421ee72877ede504a96f6485b14b537ba7e7c0b65R28.
This code appends the return type to the signature being built, prefixed with an "arrow".
The linked change replaces the -> plain ASCII arrow with the Unicode arrow →.
Afterwards, the signature is mangled by Sphinx's autodoc mangle_signature.

The problem is that this Sphinx's method expect the return type to be appended with an ASCII arrow.
Then, its regexes fail and we and up with what I showed above.

Replacing the Unicode arrow with the ASCII arrow fixed the problem.

Since I'm not sure why this Unicode was introduced in the first place, I don't know if this fix is enough.
It came with adding support for overloaded methods, where the list of parameters is replaced with the Unicode ellipsis character; and the arrow was replaced with the Unicode arrow at the same time.

Inspect the change linked in the issue and Sphinx autodoc's mangle_signature behavior first. Reproduce the problem with summarized functions or methods that have return types, including the overloaded-method case mentioned in the report. Done means signatures retain their parameter list while return types and overload representations remain correct.