[EPIC] Support withdrawals from L2 to L1

[theethernaut]

This epic tracks the tasks needed to be completed before deploying for phase C of the OVM trial that tests withdrawing functionality from L2 to L1.

• (MERGED) Currently everything is updated in this PR : Enable withdrawal functionality in L2 synthetix#806
  • Fix tests and coverage:
  • (FIXED) same chain multi:test.
  • coverage (>95%).
• Finalize contract renaming and conventions:
  • new contract names: SynthetixBridgeToBase, SynthetixBridgeToOptimistism.
  • resolver names: we use the ovm: and base: as prefixes, e.g. ovm:SynthetixBridgeToBase
  • Rename companion() view function: we can use explicit naming now i.e. synthetixBridgeToOptimism().
• Sync with the Optimism team regarding their contract upgrade:
  • ask for a new npm package (@eth-optimism/rollup-contracts) to reflect the new contract changes
  • update messenger interfaces (move from rollup-contracts package to contracts, release: 0.0.2-alpha.6).
    (MERGED) New messenger interface synthetix#825
  • fix same-chain multi-tests.
  • update spec tests: Update l2bridge spec tests synthetix#827 (MERGED)
• maxDeposit param should be removed: Remove maxDeposit from System settings synthetix#816 (MERGED).
• Update all L2 related tests to use smock.
• Support SNX to be deposited in L1 to be claimable on L2
  • (MERGED) PR: Send rewards into l2 synthetix#818
• Run a test release according to Phase C cheatsheet (https://docs.google.com/document/d/13976hTEnLJt3vVTi4Vbh8mQ875dq_T_70uGEQhZYRTc/):
  • get the addresses of the new messengers if available before phase C deployment.
  • handle it to the front end team for testing.