adds back ErasureMeta::first_coding_index field (backport #21623)

[mergify]

This is an automatic backport of pull request #21623 done by Mergify.
Cherry-pick of 49ba09b has failed:

On branch mergify/bp/v1.8/pr-21623
Your branch is up to date with 'origin/v1.8'.

You are currently cherry-picking commit 49ba09b33.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   ledger/src/blockstore_meta.rs
	modified:   ledger/src/erasure.rs
	modified:   ledger/src/shred.rs

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   ledger/src/blockstore.rs

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[mergify]

automerge label removed due to a CI failure

[mergify]

automerge label removed due to a CI failure

[mergify]

automerge label removed due to a CI failure

[codecov]

Codecov Report

Merging #22912 (858c14d) into v1.8 (add26be) will increase coverage by 0.0%.
The diff coverage is 92.4%.

@@           Coverage Diff           @@
##             v1.8   #22912   +/-   ##
=======================================
  Coverage    81.6%    81.6%           
=======================================
  Files         464      464           
  Lines      131709   131738   +29     
=======================================
+ Hits       107555   107598   +43     
+ Misses      24154    24140   -14     

[github-actions]

This PR has been automatically locked since there has not been any activity in past 14 days after it was merged.