[fix][broker] Fix possible mark delete NPE when batch index ack is enabled

[BewareMyPower]

Motivation

MLPendingAckStoreTest#testMainProcess will fail by NPE if batch index ACK is enabled. The NPE happens when the position argument does not has a non-null ackSet.

Modifications

• Add an ackBatchPosition method to handle Optional objects correctly with elegant and clear code.
• Replace BitSetRecyclable with BitSet as the value type of batchDeletedIndexes to simplify the unnecessarily complicated code of calling recycle(). For example, if recycle() is called in a callback of ConcurrentSkipListMap#compute, it could be called multiple times. Additionally, the optimization for GC is not provided because BitSetRecyclable cannot avoid the memory allocation of its underlying long arrays.
• Mark batchDeletedIndexes as @Nullable and check if it's not null instead of getConfig().isDeletionAtBatchIndexLevelEnabled() to eliminate all NPE warnings.

Verifying this change

Enable batch index ACK in MLPendingAckStoreTest and guarantee this test passes.

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[dao-jun]

lgtm

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 75.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 74.14%. Comparing base (bbc6224) to head (664fe46).
Report is 846 commits behind head on master.

Files with missing lines	Patch %	Lines
...che/bookkeeper/mledger/impl/ManagedCursorImpl.java	75.00%	5 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #23833      +/-   ##
============================================
+ Coverage     73.57%   74.14%   +0.57%     
+ Complexity    32624    32187     -437     
============================================
  Files          1877     1853      -24     
  Lines        139502   143562    +4060     
  Branches      15299    16302    +1003     
============================================
+ Hits         102638   106444    +3806     
+ Misses        28908    28727     -181     
- Partials       7956     8391     +435     

Flag	Coverage Δ
inttests	26.67% <35.71%> (+2.09%)	⬆️
systests	23.15% <35.71%> (-1.18%)	⬇️
unittests	73.67% <75.00%> (+0.82%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
...rg/apache/bookkeeper/mledger/impl/AckSetState.java	100.00% <ø> (ø)
...che/bookkeeper/mledger/impl/ManagedCursorImpl.java	79.20% <75.00%> (-0.10%)	⬇️

... and 1031 files with indirect coverage changes