[REVIEW] Add filter_characters_of_type strings API

[davidwendt]

Closes #5520

Create a new strings API that can filter characters from strings by specifying the character types.
Also, allows for an optional replacement character or string in place of each removed character.

[codecov]

Codecov Report

Merging #5666 into branch-0.15 will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##           branch-0.15    #5666   +/-   ##
============================================
  Coverage        86.25%   86.25%           
============================================
  Files               72       72           
  Lines            12672    12676    +4     
============================================
+ Hits             10930    10934    +4     
  Misses            1742     1742           

Impacted Files	Coverage Δ
python/cudf/cudf/core/column/string.py	86.57% <100.00%> (+0.07%)	⬆️

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[cwharris]

Do we want to include benchmarks for strings features?

[davidwendt]

Do we want to include benchmarks for strings features?

Argh. I keep forgetting about the benchmarks. I need to create an issue to add these.