Keep doc-string order for shape or exact props

[CNFeffery]

In developing custom components, parameters defined by PropTypes.shape or PropTypes.exact should ensure that the automatically generated doc-string follows the original order in the source code.

Closes #2990

[T4rk1n]

Looks good, just a couple comments and missing a changelog entry.

[T4rk1n]

There is failure in unit test that check for hardcoded values that needs to be updated:

    5 failed
     - tests/unit/development/test_generate_class.py:105 test_docstring
     - tests/unit/development/test_generate_class_file.py:64 test_class_string
     - tests/unit/development/test_generate_class_file.py:73 test_class_file
     - tests/unit/development/test_metadata_conversions.py:77 test_docstring
     - tests/unit/development/test_metadata_conversions.py:87 test_docgen_to_python_args

For the first three. just need to copy the new generated content and paste it on: https://github.com/plotly/dash/blob/2ec3f5ccc6b0869f41bf6919994a08f7c24332b6/tests/unit/development/metadata_test.py

metadata_conversion can change the order of the docstrings:

dash/tests/unit/development/test_metadata_conversions.py

Lines 29 to 65 in 49a80bb

	"optionalObjectWithExactAndNestedDescription",
	"\n".join(
	[
	"dict with keys:\n",
	" - color (string; optional)\n",
	" - figure (dict; optional):",
	" Figure is a plotly graph object.\n",
	" `figure` is a dict with keys:\n",
	# noqa: E501
	" - data (list of dicts; optional):",
	" data is a collection of traces.\n",
	" - layout (dict; optional):",
	" layout describes the rest of the figure.\n",
	# noqa: E501
	" - fontSize (number; optional)",
	]
	),
	],
	[
	"optionalObjectWithShapeAndNestedDescription",
	"\n".join(
	[
	"dict with keys:\n",
	" - color (string; optional)\n",
	" - figure (dict; optional):",
	" Figure is a plotly graph object.\n",
	" `figure` is a dict with keys:\n",
	# noqa: E501
	" - data (list of dicts; optional):",
	" data is a collection of traces.\n",
	" - layout (dict; optional):",
	" layout describes the rest of the figure.\n",
	# noqa: E501
	" - fontSize (number; optional)",
	],
	),
	],

[T4rk1n]

💃 Looks good, thank you.