Move fresh names from namer to codegen

Namer already generates fresh names (if there are multiple definitions in the same scope).
This is way overloaded definitions can be uniquely addressed.

However, this is confusing responsibilities. Making generated names unique should be a part of code-generation.
The job of namer is to resolve names to unique _symbols_, not to also introduce unique _names_.

Start by locating the namer and codegen phases, then trace where fresh names are generated and where names are resolved to unique symbols. The work is done when generated-name uniqueness belongs to code generation, namer only resolves symbols, and overloaded definitions in one scope remain uniquely addressable.

Written by the indexing model from the issue text.