Use bit_slice in combine_option_bitmap

[jhorstmann]

Which issue does this PR close?

Closes #1899.

Rationale for this change

The buffers are storing validity bits and there the offset has to be interpreted as number of bits instead of bytes when slicing.

What changes are included in this PR?

Are there any user-facing changes?

No

[codecov-commenter]

Codecov Report

Merging #1900 (eaefe40) into master (fc4044f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #1900   +/-   ##
=======================================
  Coverage   83.43%   83.43%           
=======================================
  Files         203      203           
  Lines       56969    56993   +24     
=======================================
+ Hits        47531    47553   +22     
- Misses       9438     9440    +2     

Impacted Files	Coverage Δ
arrow/src/compute/util.rs	99.10% <100.00%> (+0.10%)	⬆️
parquet_derive/src/parquet_field.rs	65.75% <0.00%> (-0.46%)	⬇️

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[tustvold]

Integration test failures seem unrelated, so getting this one in.