[SDK-3735] Create tree-shakable Crypto module

[lawrence-forooghian]

Note: This PR is based on top of #1417; please review that one first.

This encapsulates the crypto functionality in a tree-shakable module. See commit messages for more details.

BaseRest: 87.17 KiB
BaseRest + Rest: 87.17 KiB
BaseRest + Crypto: 90.70 KiB
BaseRest + generateRandomKey: 90.73 KiB
BaseRest + getDefaultCryptoParams: 90.73 KiB
BaseRest + decodeMessage: 87.53 KiB
BaseRest + decodeEncryptedMessage: 91.05 KiB
BaseRest + decodeMessages: 87.64 KiB
BaseRest + decodeEncryptedMessages: 91.16 KiB
BaseRealtime: 144.00 KiB
BaseRealtime + Rest: 152.65 KiB
BaseRealtime + Crypto: 147.53 KiB
BaseRealtime + generateRandomKey: 147.56 KiB
BaseRealtime + getDefaultCryptoParams: 147.56 KiB
BaseRealtime + decodeMessage: 144.36 KiB
BaseRealtime + decodeEncryptedMessage: 147.88 KiB
BaseRealtime + decodeMessages: 144.46 KiB
BaseRealtime + decodeEncryptedMessages: 147.99 KiB
generateRandomKey: 73.80 KiB
generateRandomKey + Crypto: 73.80 KiB
getDefaultCryptoParams: 73.80 KiB
getDefaultCryptoParams + Crypto: 73.80 KiB
decodeMessage: 70.61 KiB
decodeEncryptedMessage: 74.13 KiB
decodeEncryptedMessage + Crypto: 74.13 KiB
decodeMessages: 70.71 KiB
decodeEncryptedMessages: 74.23 KiB
decodeEncryptedMessages + Crypto: 74.23 KiB

Resolves #1396.

[owenpearson]

Looks good overall, one question though: