Implement usage of 'or' on an assignment

[luc10921]

Summary or solution description
I couldn't find how this type of operation was called on Python, but this is called a Elvis Operator

How to Reproduce

neo3-boa/boa3_test/test_sc/variable_test/ElvisOperatorStrParam.py

Lines 1 to 7 in 4d1558c

	from boa3.builtin.compile_time import public
	@public
	def main(param: str) -> str:
	other = param or "some default value"
	return other

Tests

neo3-boa/boa3_test/tests/compiler_tests/test_variable.py

Lines 1035 to 1052 in 4d1558c

	def test_elvis_operator_str_param(self):
	path, _ = self.get_deploy_file_paths('ElvisOperatorStrParam.py')
	runner = BoaTestRunner(runner_id=self.method_name())
	invokes = []
	expected_results = []
	invokes.append(runner.call_contract(path, 'main', 'not empty string'))
	expected_results.append('not empty string')
	invokes.append(runner.call_contract(path, 'main', ''))
	expected_results.append('some default value')
	runner.execute()
	self.assertEqual(VMState.HALT, runner.vm_state, msg=runner.error)
	for x in range(len(invokes)):
	self.assertEqual(expected_results[x], invokes[x].result)

Platform:

• OS: Windows 10 x64
• Python version: Python 3.11

[lllwvlvwlll]

Task linked: CU-864e5k912 other = s or "some default value"

[coveralls]

coverage: 92.026% (-0.04%) from 92.069%
when pulling 706f6c1 on CU-864e5k912
into 1d4cb9b on development.