Rework the patterns! macro to re-de-duplicate logic

[str4d]

The patterns! macro previously both generated the ResolvedPlatformNode::pattern_provider and ResolvedPlatformNode::enqueue_pattern_property_changes methods, and also generated some of the boilerplate methods for the #[implement(_)] derivations from the windows crate.

In windows 0.32 the implement macro was reworked to use traits (microsoft/windows-rs#1450). As a result, we can't just derive the methods for all patterns in the existing patterms! macro invocation, because:

• The per-trait methods need to go into separate impl IFooBarProvider_Impl for FooBarProvider trait impls.
• The patterns are a subset of the trait methods that need to be implemented.

In #102 I took the simple approach of duplication: we now manually implement the boilerplate methods in addition to specifying their details inside the patterns! macro. It would be nice to figure out how to rework the patterns! macro to re-introduce the previous de-duplication.

[str4d]

Aaand the moment I wrote this issue, I figured out how to do this nicely 😄 I'll update #102 with this.