Better code structure for generating pytest plugins

[MatthewFlamm]

The current code is more or less one long script. Some portions should be abstracted out for better understandability and maintainability.

For example, this code is logically separate from the rest (it only needs to know where to find the file for modification):

pytest-homeassistant-custom-component/generate_phacc/generate_phacc.py

Lines 151 to 165 in 66c8055

	# modify load_fixture
	with open(os.path.join(PACKAGE_DIR, "common.py"), "r") as original_file:
	data = original_file.readlines()
	import_time_lineno = [i for i, line in enumerate(data) if "from time" in line]
	assert len(import_time_lineno) == 1
	data.insert(import_time_lineno[0] + 1, "import traceback\n")
	load_fixture_lineno = [i for i, line in enumerate(data) if "load_fixture" in line]
	assert len(load_fixture_lineno) == 1
	data.insert(load_fixture_lineno[0] + 2, " start_path = traceback.extract_stack()[-2].filename\n")
	data[load_fixture_lineno[0] + 3] = data[load_fixture_lineno[0] + 3].replace("__file__", "start_path")
	with open(os.path.join(PACKAGE_DIR, "common.py"), "w") as new_file:
	new_file.writelines(data)