tx.GasPrice should return effectiveGasPrice or feeCap for 1559 txs

[MarekM25]

Changes:

• More info: Require gasPrice field for both legacy and EIP-1559 transactions ethereum/execution-specs#251

Types of changes

What types of changes does your code introduce?
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• 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
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Other (please describe):

Testing

Requires testing

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• No

In case you checked yes, did you write tests??

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• No