[Requires Arrow spec] Added Utf8Sequence

[jorgecarleitao]

This draft PR adds support for Utf8Sequence and LargeUtf8Sequence as described on this draft discussing additions to the arrow specification.

It won't be merged until the Arrow specification is updated (and is abandoned otherwise). I have dropped it here for two reasons:

1. offer visibility that the arrow format is considering adding new arrays (feel free to comment on the document)
2. It is a good exercise to see how far we can go when the present design is applied to future types

[codecov]

Codecov Report

Merging #784 (780bef7) into main (60130f4) will decrease coverage by 0.69%.
The diff coverage is 0.00%.

❗ Current head 780bef7 differs from pull request most recent head 157b174. Consider uploading reports for the commit 157b174 to get more accurate results

@@            Coverage Diff             @@
##             main     #784      +/-   ##
==========================================
- Coverage   71.10%   70.40%   -0.70%     
==========================================
  Files         346      319      -27     
  Lines       18956    16916    -2040     
==========================================
- Hits        13478    11910    -1568     
+ Misses       5478     5006     -472     

Impacted Files	Coverage Δ
src/array/display.rs	50.00% <0.00%> (ø)
src/array/equal/mod.rs	81.37% <0.00%> (-5.09%)	⬇️
src/array/equal/utf8_sequence.rs	0.00% <0.00%> (ø)
src/array/ffi.rs	70.00% <ø> (-5.00%)	⬇️
src/array/growable/mod.rs	21.56% <ø> (-9.92%)	⬇️
src/array/mod.rs	66.39% <0.00%> (+3.62%)	⬆️
src/array/string_sequence/iterator.rs	0.00% <0.00%> (ø)
src/array/string_sequence/mod.rs	0.00% <0.00%> (ø)
src/compute/aggregate/memory.rs	19.51% <0.00%> (-1.01%)	⬇️
src/datatypes/mod.rs	94.59% <0.00%> (-2.63%)	⬇️
... and 231 more

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