fix dyn syntax for trait objects

[jimexist]

Which issue does this PR close?

Fixes some issues from #591, mostly because for trait objects we'll have to prefix the dyn keyword which is mandatory in rust 2021 edition.

Closes #.

Rationale for this change

What changes are included in this PR?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

Merging #592 (765f744) into master (87d2840) will increase coverage by 0.00%.
The diff coverage is 54.83%.

@@           Coverage Diff           @@
##           master     #592   +/-   ##
=======================================
  Coverage   82.41%   82.41%           
=======================================
  Files         167      167           
  Lines       46232    46232           
=======================================
+ Hits        38100    38101    +1     
+ Misses       8132     8131    -1     

Impacted Files	Coverage Δ
arrow/src/array/array.rs	80.90% <ø> (ø)
arrow/src/array/transform/mod.rs	86.06% <ø> (ø)
arrow/src/compute/kernels/take.rs	94.72% <ø> (ø)
arrow/src/record_batch.rs	90.44% <ø> (ø)
arrow/src/array/builder.rs	86.11% <22.85%> (ø)
arrow/src/array/ord.rs	63.33% <83.33%> (ø)
arrow/src/array/array_binary.rs	92.23% <100.00%> (ø)
arrow/src/array/array_boolean.rs	94.01% <100.00%> (ø)
arrow/src/array/array_dictionary.rs	88.38% <100.00%> (ø)
arrow/src/array/array_list.rs	95.51% <100.00%> (ø)
... and 13 more

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[alamb]

This is awesome -- thank you @jimexist