Decoding bug: id property is lost

[springmeyer]

When an input MVT contains a property called "id", the property is discarded in the decoded MLT.

It is important that we retain all properties with full fidelity unless nesting is enabled. Otherwise styles will break that might migrate to MLT from MVT.

Note: I'm not talking about the feature.id. I'm talking about a property (aka field) called "id".

[springmeyer]

I figure that fixing this should be easy, and something I can do. It will be necessary for proper rendering of bing tiles.

@mactrem any concerns about preserving all properties, even ones named "id"?