CRAM: Refactor AlignmentSpan

[jmthibault79]

Description

Rename AlignmentSpan to SliceMetadata and Mapped/Unmapped subclasses

• make immutable
• moved much of ContainerParserTest to SliceMetadataTest
• move to new slice package
• tests

Checklist

• [x] Code compiles correctly
• [x] New tests covering changes and new functionality
• [x] All tests passing
• [x] Extended the README / documentation, if necessary
• [ ] Is not backward compatible (breaks binary or source compatibility)

[codecov-io]

Codecov Report

Merging #1260 into master will increase coverage by 0.006%. The diff coverage is 84.536%.

@@              Coverage Diff               @@
##              master    #1260       +/-   ##
==============================================
+ Coverage     69.324%   69.33%   +0.006%     
- Complexity      8287     8293        +6     
==============================================
  Files            555      557        +2     
  Lines          33075    33078        +3     
  Branches        5561     5561               
==============================================
+ Hits           22929    22933        +4     
+ Misses          7884     7880        -4     
- Partials        2262     2265        +3

Impacted Files	Coverage Δ	Complexity Δ
src/main/java/htsjdk/samtools/cram/CRAIEntry.java	68.421% <ø> (-2.632%)	17 <0> (ø)
...n/java/htsjdk/samtools/cram/structure/SliceIO.java	82.895% <ø> (ø)	14 <0> (ø)	:arrow_down:
...amtools/cram/encoding/writer/CramRecordWriter.java	89.063% <ø> (ø)	26 <0> (ø)	:arrow_down:
...ava/htsjdk/samtools/CRAMContainerStreamWriter.java	70.902% <ø> (ø)	54 <0> (ø)	:arrow_down:
...va/htsjdk/samtools/cram/structure/ContainerIO.java	60.92% <ø> (ø)	13 <0> (ø)	:arrow_down:
...rc/main/java/htsjdk/samtools/BAMIndexMetaData.java	73.832% <ø> (ø)	22 <0> (ø)	:arrow_down:
...amtools/cram/encoding/reader/CramRecordReader.java	85.256% <ø> (ø)	26 <0> (ø)	:arrow_down:
...c/main/java/htsjdk/samtools/cram/build/CramIO.java	75.51% <ø> (ø)	20 <0> (ø)	:arrow_down:
...java/htsjdk/samtools/cram/structure/Container.java	88.462% <100%> (+4.251%)	11 <3> (+3)	:arrow_up:
src/main/java/htsjdk/samtools/CRAMIterator.java	81.159% <100%> (ø)	32 <0> (ø)	:arrow_down:
... and 15 more

[jmthibault79]

Closing this for a rethink after #1266