Display to the user / expose via JSON RPC the first full state block

[tkstanczak]

Run binary search on the tree and expose the info about the first fully synced block.

[kamilchodola]

Interesting idea. Always struggle just by logs to see at which exact point my node "have all history" (assuming pruning is disabled).
I think it is a good first issue.

@MarekM25

[kamilchodola]

@Scooletz Low priority in terms of needs - but very good for QA team to have sth like this so in free time maybe you could check on that.

[obchain]

Hi maintainers — happy to take this. Plan is to binary-search the trie for the first block with a fully synced state and expose it via a JSON-RPC method (eth/debug namespace TBD based on review preference). Will follow with a PR + tests.

[svlachakis]

closing because #11438 makes it obsolete.