core/vm: replace function precompile2 with precompile

[gzliudan]

Proposed changes

This PR replaces function precompile2 with precompile:

func (evm *EVM) precompile(addr common.Address) (PrecompiledContract, bool) {
	var precompiles map[common.Address]PrecompiledContract
	switch {
	case evm.chainRules.IsXDCxDisable:
		precompiles = PrecompiledContractsXDCv2
	case evm.chainRules.IsIstanbul:
		precompiles = PrecompiledContractsIstanbul
	case evm.chainRules.IsByzantium:
		precompiles = PrecompiledContractsByzantium
	default:
		precompiles = PrecompiledContractsHomestead
	}
	p, ok := precompiles[addr]
	return p, ok
}

func (evm *EVM) precompile2(addr common.Address) (PrecompiledContract, bool) {
	var precompiles map[common.Address]PrecompiledContract
	switch {
	case evm.chainRules.IsXDCxDisable:
		precompiles = PrecompiledContractsXDCv2
	case evm.chainRules.IsIstanbul && evm.ChainConfig().IsTIPXDCXCancellationFee(evm.BlockNumber):
		precompiles = PrecompiledContractsIstanbul
	case evm.chainRules.IsByzantium:
		precompiles = PrecompiledContractsByzantium
	default:
		precompiles = PrecompiledContractsHomestead
	}
	p, ok := precompiles[addr]
	return p, ok
}

The conditions evm.chainRules.IsIstanbul and evm.ChainConfig().IsTIPXDCXCancellationFee(evm.BlockNumber) are same because:

func (c *ChainConfig) IsIstanbul(num *big.Int) bool {
	return isForked(common.TIPXDCXCancellationFee, num) || isForked(c.IstanbulBlock, num)
}

func (c *ChainConfig) IsTIPXDCXCancellationFee(num *big.Int) bool {
	return isForked(common.TIPXDCXCancellationFee, num)
}

Types of changes

What types of changes does your code introduce to XDC network?
Put an ✅ in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation Update (if none of the other choices apply)
• Regular KTLO or any of the maintaince work. e.g code style
• CICD Improvement

Impacted Components

Which part of the codebase this PR will touch base on,

Put an ✅ in the boxes that apply

• Consensus
• Account
• Network
• Geth
• Smart Contract
• External components
• Not sure (Please specify below)

Checklist

Put an ✅ in the boxes once you have confirmed below actions (or provide reasons on not doing so) that

• This PR has sufficient test coverage (unit/integration test) OR I have provided reason in the PR description for not having test coverage
• Provide an end-to-end test plan in the PR description on how to manually test it on the devnet/testnet.
• Tested the backwards compatibility.
• Tested with XDC nodes running this version co-exist with those running the previous version.
• Relevant documentation has been updated as part of this PR
• N/A

[wanwiset25]

It doesn't matter now because the fork block have passed, but minor nitpick:
the condition is not exactly the same because in precompile2 it is && condition while in IsIstanbul it is || condition.

[gzliudan]

func (c *ChainConfig) IsIstanbul(num *big.Int) bool {
	return isForked(common.TIPXDCXCancellationFee, num) || isForked(c.IstanbulBlock, num)
}

The old version is:

func (c *ChainConfig) IsIstanbul(num *big.Int) bool {
	return isForked(common.TIPXDCXCancellationFee, num)
}

I change it to:

return isForked(common.TIPXDCXCancellationFee, num) || isForked(c.IstanbulBlock, num)

for other purpose in a PR ago.