Issue 5460: (SLTS) Add read index virtual block entries to metadata.

[sachin-j-joshi]

Signed-off-by: Sachin Joshi sachin.joshi@emc.com

Change log description
Persistent custom skip list like sparse index entries.

Purpose of the change
Fixes #5460

What the code does
Add custom skip list index metadata using following logic

• The segment is imagined to divided into fixed size virtual block ( defined in config say 64MB).
• For each multiple of fixed block size (eg 1B, 2B, 3B etc) add a metadata entry to table store that points to the chunk that contains the first byte in that virtual block.
• Use virtual block index entry during read.
• Update write, delete concat , truncate logic to keep these up to date.

How to verify it
All tests must pass

[codecov]

Codecov Report

Merging #5461 (1466105) into master (8b88628) will decrease coverage by 0.00%.
The diff coverage is 91.11%.

@@             Coverage Diff              @@
##             master    #5461      +/-   ##
============================================
- Coverage     84.78%   84.78%   -0.01%     
- Complexity    13905    13925      +20     
============================================
  Files           917      918       +1     
  Lines         51517    51635     +118     
  Branches       5312     5321       +9     
============================================
+ Hits          43677    43777     +100     
- Misses         4955     4968      +13     
- Partials       2885     2890       +5     

Impacted Files	Coverage Δ	Complexity Δ
...col/src/main/java/io/pravega/shared/NameUtils.java	89.57% <0.00%> (-0.56%)	65.00 <0.00> (ø)
...segmentstore/storage/chunklayer/ReadOperation.java	86.77% <81.81%> (-3.82%)	44.00 <3.00> (+4.00)	⬇️
...tore/storage/chunklayer/ChunkedSegmentStorage.java	90.02% <89.65%> (-0.12%)	118.00 <7.00> (+6.00)	⬇️
...segmentstore/storage/chunklayer/ChunkIterator.java	95.23% <90.90%> (-4.77%)	7.00 <3.00> (+1.00)	⬇️
...store/storage/metadata/ReadIndexBlockMetadata.java	90.90% <90.90%> (ø)	6.00 <6.00> (?)
...tstore/storage/chunklayer/DefragmentOperation.java	95.94% <95.83%> (-0.12%)	48.00 <3.00> (+3.00)	⬇️
...torage/chunklayer/ChunkedSegmentStorageConfig.java	98.24% <100.00%> (+0.09%)	3.00 <0.00> (ø)
...gmentstore/storage/chunklayer/ConcatOperation.java	92.30% <100.00%> (+0.38%)	28.00 <0.00> (ø)
...egmentstore/storage/chunklayer/ReadIndexCache.java	82.97% <100.00%> (+0.37%)	25.00 <0.00> (+1.00)
...entstore/storage/chunklayer/TruncateOperation.java	93.85% <100.00%> (+0.10%)	33.00 <0.00> (ø)
... and 22 more

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