Output pyish versions of objects using legacy override flag

[jasmith-hs]

This is mainly a PR for eager execution, but it also refactors the usePyishObjectMapper flag.
Only output the pyish version of an object to the rendered output if usePyishObjectMapper is true. Previously, in eager execution, whenever something like {{ foo }} was rendered, it would output the pyish version. If it were a map, it would look like:

{'a': some a', 'b': 'some b'}

But with default jinjava and the default value for this flag, it would output like:

{a=some a, b=some b}

This PR makes eager execution output respect that flag the same way that default jinjava execution does. usePyishObjectMapper is also refactored to be in the LegacyOverrides builder because it is a legacy functionality override.