Code PR

• I have read through thecontributing notes and understand the structure of the package. In particular, if my PR modifies code ofplotly.graph_objects, my modifications concern thecodegen files and not generated files.
• I have added tests (if submitting a new feature or correcting a bug) or
  modified existing tests.
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Refactor of validators

This refactor is based onrelease-6.0.1rc0

Helps address#1208

Motivation

The large number of files in theplotly/validators folder slows down package installation, esp. on systems where files are inspected for viruses during install (e.g. Windows)

The majority of the code is duplicated across these files as well, as there are e.g. >650 instances of nearly-identical classes inheriting_plotly_utils.basevalidators.BooleanValidator

Mitigation

Things to note, in the current validator arrangement:

1. Nearly all the validator classes inplotly.validators inherit directly from classes in_plotly_utils.basevalidators
2. None of them override any methods at all, they just provide custom kwargs to__init__
3. Almost all access to the validators in the codebase is through theplotly.validator_cache.ValidatorCache.get_validator(parent_name, prop_name)
4. All these validator python source modules aregenerated by the plotly build system, by runningpython commands.py codegen

In this PR, the following changes are made:

1. Duringcodegen, instead of generating and writing thousands of python files toplotly/validators/..., we create a single JSON file store atplotly/validators/_validators.json and for each(parent_name, prop_name) combination we add an entry to the store with
   • "superclass": the name of the validator class to instantiate
   • "params": the custom kwargs to use when instantiating the validator class
2. TheValidatorCache.get_validator method is modified so that rather than calculating an import path and then importing a validator class from the file tree, it looks up the custom kwargs and validator class name from the JSON store, then creates (and caches) a new instance of the validator class from
   basevalidators, with the custom init kwargs, finally returning the instance
3. Usages of direct import of validator classes fromplotly.validators in the codebase are refactored to use theValidatorCache instead (there were only a handful of these cases)

The net result is that the number of files to be installed is reduced from 14981 to 1652.