Small refactoring in effect metadata

[TimvdLippe]

Refactor effect metadata system with a couple of modifications:

• Add fallback for when data does not exist. This is primarily the start for Implement build time optimizations #4137 and potential later changes to choose better defaults to reduce memory
• Factor out the effect functions from property-effects. This is primarily a readibility improvement.
• Rewrite findTemplateNode to operate on an array instead of nested objects. This stores significantly less information in a compressed format.

Reference Issue

These are preparations #4137

[TimvdLippe]

As this PR grew big over time, I am factoring out some of the sub-changes. This makes reviewing easier and make sure that the changes are not all-or-nothing, but pick those that we like.

I extracted the findTemplateNode change to #4853

[sorvell]

Since there are potentially breaking changes in this PR, we are likely to consider it for Polymer 3.x.

[TimvdLippe]

Closing the PR for now, but keeping the branch alive. We will revisit this for Polymer 3.