[generator] Fix Formatted() overloads & parameter aliases (#185)

[luhenry]

Fixes: https://bugzilla.xamarin.com/show_bug.cgi?id=59472

Assume you have the following Java method:

	class Example {
		public static CharSequence identity(CharSequence value) {
			return value;
		}
	}

When binding Example.identity(), we will rename it to have a
Formatted suffix, and "overload" it with a string overload:

	partial class Example {
		public static ICharSequence IdentityFormatted (ICharSequence value)
		{
			// ...
		}

		public static string Identity (string value)
		{
			// ...
		}
	}

The purpose of this overloading is to make it easier to call the
method from C# code. It's not currently possible for interfaces to
contain static methods, which in turn means it's not possible for
interfaces to contain conversion operators. Thus, if a C# developer
wants to do:

Example.Identity ("value");

there would be no way to have this Just Work™ while having only
ICharSequence running around.

(Additionally, we rename the method so that we don't need to worry
about return types. In the above example, the return type is
converted, so if we didn't rename to IdentityFormatted(), we
couldn't overload for many interesting use cases.)

This feature has existed for quite some time, but there's a bug:
Example.Identity() would do:

	partial class Example {
		public static string Identity (string value)
		{
			var jls_value = value == null ? null : new Java.Lang.String (value)
			var __result  = IdentityFormatted (jls_value);
			jls_value?.Dispose ();
			return __result?.ToString ();
		}
	}

This seems acceptable, but this will break when
Example.IdentityFormatted() -- Example.identity() -- returns the
parameter. When that happens, jls_value and __result are
the same instance, and thus the jls_value?.Dispose() also
disposes of __result. In this case, __result.ToString() will be
null, which is not what is desired.

The fix is to grab __result.ToString() before disposing of the
temporary parameters:

	partial class Example {
		public static string Identity (string value)
		{
			var jls_value = value == null ? null : new Java.Lang.String (value)
			var __result  = IdentityFormatted (jls_value);
			var __rsval   = __result?.ToString ();
			jls_value?.Dispose ();
			return __rsval;
		}
	}

This way we ensure that we get a copy before the source is disposed.

[dnfclas]

@luhenry,
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[jonpryor]

1. When did you create the mono-2017-10 branch?
2. How did (1) not include a commit from 2.5 weeks ago?
3. You should probably just directly cherry-pick fixes to a development branch like mono-2017-10.

[luhenry]

This PR was created by accident (hub gone wrong), so let me close it