Refactor proxy with diamond pattern

[yrong]

Context

When implementing transfer polkadot assets it seems the Gateway code size exceeds 24576 bytes.

Contract	Size (kB)	Margin (kB)
Gateway	24.759	-0.183
...	...	...

Considering more features(e.g. Transacts) will be added soon, a single Gateway with all interfaces may not be ideal. So in this PR we change the proxy pattern from the previous EIP-1967 to EIP-2535(the diamond way) and split outbound interfaces to a separate contract(facet).

Though it solves the issue of the contract size limit it's not perfect, it costs more gas and is more complicated.

[codecov]

Codecov Report

Attention: Patch coverage is 47.43590% with 82 lines in your changes are missing coverage. Please review.

Project coverage is 66.08%. Comparing base (6212597) to head (24787df).

Files	Patch %	Lines
contracts/src/storage/DiamondStorage.sol	23.91%	63 Missing and 7 partials ⚠️
contracts/src/Gateway.sol	73.91%	4 Missing and 2 partials ⚠️
contracts/src/GatewayOutbound.sol	90.90%	2 Missing and 1 partial ⚠️
contracts/src/GatewayProxy.sol	50.00%	1 Missing and 1 partial ⚠️
contracts/src/DeployGatewayLogic.sol	0.00%	1 Missing ⚠️

Additional details and impacted files

@@                         Coverage Diff                         @@
##           ron/polkadot-assets-on-ethereum    #1162      +/-   ##
===================================================================
- Coverage                            72.79%   66.08%   -6.72%     
===================================================================
  Files                                   15       17       +2     
  Lines                                  522      625     +103     
  Branches                                98      125      +27     
===================================================================
+ Hits                                   380      413      +33     
- Misses                                 115      174      +59     
- Partials                                27       38      +11     

Flag	Coverage Δ
solidity	66.08% <47.43%> (-6.72%)	⬇️

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