* [Python] Fix various codegen problems.
This includes:
- escaping keywords happens **after** converting the case:
- currently, `table ClassT` generate `class = Class()` which is invalid Python;
- imports in `one_file` mode use the filename rather than the type name when resolving module names;
- use `filename_suffix` instead of the hardcoded `_generated` one;
- generate empty files if no structs or enums are available. This makes the set of output files more predictable for Bazel.
* [Python] Fix various codegen problems.
This includes:
- escaping keywords happens **after** converting the case:
- currently, `table ClassT` generate `class = Class()` which is invalid Python;
- imports in `one_file` mode use the filename rather than the type name when resolving module names;
- use `filename_suffix` instead of the hardcoded `_generated` one;
- generate empty files if no structs or enums are available. This makes the set of output files more predictable for Bazel.
