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ARROW-7921: [Go] Add Reset method to various components and clean up comments.

The reset method allow the data structures to be re-used so they don't have to be allocated over and over again.

Closes #6430 from richardartoul/ra/merge-upstream and squashes the following commits:

5a0828187 <Richard Artoul> Add license to test file
d76be05ca <Richard Artoul> Add test for data reset
d102b1fff <Richard Artoul> Add tests
d3e6e6785 <Richard Artoul> cleanup comments
c8525aece <Richard Artoul> Add Reset method to int array (#5)
489ca2593 <Richard Artoul> Fix array.setData() to retain before release (#4)
88cd05ff8 <Richard Artoul> Add reset method to Data (#3)
6d1b2775c <Richard Artoul> Add Reset() method to String array (#2)
dca230383 <Richard Artoul> Add Reset method to buffer and cleanup comments (#1)

Lead-authored-by: Richard Artoul <richard.artoul@datadoghq.com>
Co-authored-by: Richard Artoul <richardartoul@gmail.com>
Signed-off-by: Sebastien Binet <binet@cern.ch>