QuantileStateCoder should be a StandardCoder

[kennknowles]

The issue is that the coder does not report component encodings which prevents effective runner inspection of the components.

Imported from Jira BEAM-466. Original Jira may contain additional context.
Reported by: lcwik.

[algorithmor]

Newbie here trying to help. I was going through the codebase and found following info.

2d13bac renamed StandardCoder to StructuredCoder
cbcec7c converted most of the standard coders to CustomCoders

So, is the goal in this issue now that QuantileStateCoder should be a StructuredCoder or should it be a CustomCoder?

[kennknowles]

Ah yes. The goal is to make everything a StructuredCoder so it can have a representation that a runner understands.

Noting that this tag of "backwards incompatible" means the change might be tricky.