If #to_proc is defined, this uses the following error message format,
matching the error message format used for * when to_a returns non-Array
and for ** when to_hash returns non-Hash:

```
can't convert ClassName to Proc (ClassName#to_proc gives OtherClassName)
```

If #to_proc is not defined, this uses the following error message format,
matching the error message format used when ** is called on a non-Hash
not implementing to_hash.

```
no implicit conversion of ClassName into Proc
```

There isn't a similar error for * when called on a non-Array not
implementing to_a, as Ruby does not raise for that case.

Fixes [Bug #21563]

[Feature #13557]

Setting the backtrace with an array of strings is lossy. The resulting
exception will return nil on `#backtrace_locations`.

By accepting an array of `Backtrace::Location` instance, we can rebuild
a `Backtrace` instance and have a fully functioning Exception.

Co-Authored-By: Étienne Barrié <etienne.barrie@gmail.com>

[Feature #16495]

Before this commit, the test fails with RGENGC_CHECK_MODE enabled:

    TestException#test_detailed_message_under_gc_compact_stress [test/ruby/test_exception.rb:1466]:
    <"\e[1mfoo (\e[1;4mRuntimeError\e[m\e[1m)\e[m\n" +
    "\e[1mbar\e[m\n" +
    "\e[1mbaz\e[m"> expected but was
    <"\e[1mfoo (\e[1;4mRuntimeError\e[m\e[1m)\e[m\n" +
    "\e[1m\x00\x00\x00\x00\x00\x00\x00\e[m">.