feat: add LDValueConverter and LDContextEncoder to common #562

Job	Run time
test-packaging	4m 47s
test-contract-tests	4m 25s
test-platforms-and-versions (ubuntu-latest, 17)	4m 0s
test-platforms-and-versions (ubuntu-latest, 11)	4m 3s
test-platforms-and-versions (ubuntu-latest, 19)	3m 59s
test-platforms-and-versions (ubuntu-latest, 8)	3m 44s
	24m 58s

Provide feedback