fix: signature helper

[camilledejoye]

I noticed there was a problem when an argument was a string containing a comma:
The argument count was off because the comma was interpreted as an argument separator.

So I tried to look around for examples on uncommon cases that might not been handled: nested calls, multiline arguments, etc.
I found some cases that was not handled so add a few more tests.

I try to explain my logic when it come to solving the issues in the commit message, don't hesitate to check it out.

There one case that might be a personal preference and I don't know how it should behave.
So any one reading this, please gave us your opinion so we can try to choose the more commonly accepted behavior:

<?php
function hello(string $foo, int $bar) {};
function goodbye(string $good, int $by) {};
hello(
    "hello",
    goo<>dbye("good", "by")
);

<> being the cursor position when we ask for the signature to be resolved.
I personally expect to have this result:

hello(string $foo, int $bar)

But I get that it can be confusing since:

<?php
function hello(string $foo, int $bar) {};
he<>llo("hello", 1);

Would resolved as:

hellow(string $foo, int $bar)

I guess it can be sum up to, would you gave the priority to resolve the signature of:

• the call expression the cursor is on
• the call expression the cursor is inside of