Extend set of valid FASTA format file extensions

[sjaenick]

Description

Please explain the changes you made here.

The set of recognized file extensions for the FASTA format was extended, adding in .fas and .fas.gz.

Explain the motivation for making this change. What existing problem does the pull request solve?

.fas is a widely used extension for FASTA-formatted files. In previous htsjdk releases, the set of file extensions used to be modifiable, so we could add additional suffices at runtime. Since this has been changed to an unmodifiable set, this is no longer an option. .fas (and .fas.gz) are pretty common enough to warrant inclusion into the set of predefined extensions.

Things to think about before submitting:

• [x] Make sure your changes compile and new tests pass locally.
• [ ] Add new tests or update existing ones:
  • A bug fix should include a test that previously would have failed and passes now.
  • New features should come with new tests that exercise and validate the new functionality.
• [ ] Extended the README / documentation, if necessary
• [x] Check your code style.
• [x] Write a clear commit title and message
  • The commit message should describe what changed and is targeted at htsjdk developers
  • Breaking changes should be mentioned in the commit message.

[codecov-commenter]

Codecov Report

Merging #1495 into master will decrease coverage by 0.006%. The diff coverage is n/a.

@@               Coverage Diff               @@
##              master     #1495       +/-   ##
===============================================
- Coverage     69.279%   69.273%   -0.006%     
+ Complexity      8764      8763        -1     
===============================================
  Files            590       590               
  Lines          34755     34755               
  Branches        5800      5800               
===============================================
- Hits           24078     24076        -2     
- Misses          8386      8387        +1     
- Partials        2291      2292        +1     

Impacted Files	Coverage Δ	Complexity Δ
...main/java/htsjdk/samtools/util/FileExtensions.java	80.000% <ø> (ø)	1.000 <0.000> (ø)
...htsjdk/samtools/util/nio/DeleteOnExitPathHook.java	80.952% <0.000%> (-9.524%)	3.000% <0.000%> (-1.000%)