MenuItem conflict with specifity of Menu sub selector

[SimeonC]

tablekit/system/react/src/components/MenuList.ts

Lines 24 to 27 in 464aefb

	'& > li > *': {
	flex: '1 1 100%',
	justifyContent: 'flex-start'
	}

In the above-linked code the specificity of this selector means that the MenuItem cannot be overwritten in styles. We need to move this style to the MenuItem styles specifically.