[generator] Fix localization error.

[jpobst]

In #689 we made generator localizable. One of the changes was this pattern:

- Report.Warning (0, Report.WarningReturnValue + 0, "Unknown return type {0} {1}.", java_type, context.ContextString);
+ Report.LogCodedWarning (0, Report.WarningUnknownReturnType, java_type, context.ContextString);

where:
Report.WarningUnexpectedFieldType = "Unknown return type '{0}' for member '{1}'."

However context.ContextString generates a hard to localize string like:

in method CreateFromXml in managed type Android.Content.Res.ColorStateList

resulting in warnings like this:

warning BG8800: Unknown return type 'System.Xml.XmlReader' for member 'in method CreateFromXml in managed type Android.Content.Res.ColorStateList'.

Instead, create a context.ContextTypeMember method that formats the member as just a type signature, which fits the localized message:

warning BG8800: Unknown return type 'System.Xml.XmlReader' for member 'Android.Content.Res.ColorStateList.CreateFromXml'.

[jonpryor]

When ContextMethod isn't null, could this also include the parameter list?

The example in the PR message, ColorStateList.CreateFromXml(), contains two overloads. It would presumably be helpful/useful if the warning message mentioned which overload was at fault:

warning BG8800: Unknown return type 'System.Xml.XmlReader' for member 'Android.Content.Res.ColorStateList.CreateFromXml(Android.Content.Res.Resources, System.Xml.XmlReader)'.

[jonpryor]

Considering that this method performs a string allocation, should it perhaps instead be a GetContextTypeMember() method?

[jonpryor]

Squash-and-merge message:

In d664e90e we made `generator` localizable.  One of the changes was
this pattern:

	- Report.Warning (0, Report.WarningReturnValue + 0, "Unknown return type {0} {1}.", java_type, context.ContextString);
	+ Report.LogCodedWarning (0, Report.WarningUnknownReturnType, java_type, context.ContextString);

in which `Report.WarningUnknownReturnType` is:

	"Unknown return type '{0}' for member '{1}'."

However `context.ContextString` generates a hard to localize string, e.g.

	in method CreateFromXml in managed type Android.Content.Res.ColorStateList

resulting in messages such as:

	warning BG8800: Unknown return type 'System.Xml.XmlReader' for member 'in method CreateFromXml in managed type Android.Content.Res.ColorStateList'.

This message doesn't "look right", nor is it itself localizable.

Instead, add a `context.GetContextTypeMember ()` method which formats the
member as a type signature, which doesn't need to be separately
localized and "reads correctly" in context:

	warning BG8800: Unknown return type 'System.Xml.XmlReader' for member 'Android.Content.Res.ColorStateList.CreateFromXml(Android.Content.Res.Resources, System.Xml.XmlReader)'.

Note that ^^ requires that ContextTypeMember actually include method parameter types. If that isn't done, the message should be updated accordingly.

[jonpryor]

The p.RawType here confuses me.

For starers, I can't find it?

% git grep 'RawType' 
tests/Xamarin.Android.Tools.ApiXmlAdjuster-Tests/api-24.xml.in:        name="getRawType"

(Yet the PR builds, which makes this even more confusing to me.)

Secondly, do we want the "signature" to contain Java names or C# names? I'd think we'd want the Parameter.Type property?

https://github.com/xamarin/java.interop/blob/f6c12ba30048748572af57654b218c60bc9ff95f/tools/generator/Java.Interop.Tools.Generator.ObjectModel/Parameter.cs#L222-L226

[jpobst]

This point of the process is looking up Java types (type) and converting them to C# types (sym). So sym is still null, causing an NRE if we use Parameter.Type.