Contracts read/write: method_id instead function_name as a key

[vbaranov]

Motivation

https://blockscout.com/poa/sokol/address/0xD99dFe5F3253CDACd1C4eCe0Da524187fD9EacF4/contracts

Changelog

Add method id as key in the list of contract methods instead of function name

Checklist for your Pull Request (PR)

• I added an entry to CHANGELOG.md with this PR
• If I added new functionality, I added tests covering it.
• If I fixed a bug, I added a regression test to prevent the bug from silently reappearing again.
• I checked whether I should update the docs and did so by submitting a PR to https://github.com/blockscout/docs
• If I added/changed/removed ENV var, I submitted a PR to https://github.com/blockscout/docs to update the list of env vars at https://github.com/blockscout/docs/blob/master/for-developers/information-and-settings/env-variables.md and I updated the version to master in the Version column. Changes will be reflected in this table: https://docs.blockscout.com/for-developers/information-and-settings/env-variables.
• If I add new indices into DB, I checked, that they are not redundant with PGHero or other tools

[github-actions]

Pull Request Test Coverage Report for Build 6260052447415ef1b3d23b168159645dfa286d80-PR-3257

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-20.01%) to 53.526%

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Totals
Change from base Build 61f43bf111711d6c557e52c66867611962f2cb44:	-20.01%
Covered Lines:	425
Relevant Lines:	794

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💛 - Coveralls