Add Blockstore::get_rooted_block_with_entries method

[CriesofCarrots]

Problem

There is interest in storing entry data in BigTable for redundancy. The BigTable uploader uses Blockstore::get_rooted_block() which flattens all the transactions in the block. But since it's already looping through all entries, this seems like the right place to collect Entry data as well.

Summary of Changes

Add helper structs and method to support a new Blockstore::get_rooted_block_with_entries()

[codecov]

Codecov Report

Merging #33995 (5bce7e4) into master (06884a0) will decrease coverage by 0.1%.
Report is 6 commits behind head on master.
The diff coverage is 56.2%.

@@            Coverage Diff            @@
##           master   #33995     +/-   ##
=========================================
- Coverage    81.9%    81.9%   -0.1%     
=========================================
  Files         811      811             
  Lines      219339   219366     +27     
=========================================
+ Hits       179699   179717     +18     
- Misses      39640    39649      +9     

[steviez]

LGTM! Apologies for the wild goose chase on one or two of those comments!