forms.JSONField crashes with RecursionError on deeply nested input

[Philip Sørensen]

forms.JSONField.to_python() and bound_data() only catch json.JSONDecodeError. When the submitted value is nested more deeply than the recursion limit, json.loads() raises RecursionError instead, so the form crashes (HTTP 500) rather than showing "Enter a valid JSON.". About 4 KB of input is enough, well within DATA_UPLOAD_MAX_MEMORY_SIZE:

>>> from django import forms
>>> forms.JSONField().clean("[" * 100_000 + "]" * 100_000)
RecursionError: maximum recursion depth exceeded while decoding a JSON array from a unicode string

This affects any form or ModelForm with a JSONField, including the admin. The contrib.postgres HStoreField form field has the same pattern.

Patch: also catch RecursionError in those three places, with regression tests.