[C++] Add substring count kernel

[asfimport]

Returns the number of times the specified substring occurs in the string, like Python's str.count()

Reporter: Ian Cook / @ianmcook
Assignee: David Li / @lidavidm

Related issues:

• [C++] String algorithm library for StringArray/BinaryArray (is a child of)
• [C++] Implement string/binary contains for exact matches (is related to)
• [C++] Add regex count kernel (is related to)
• [R] bindings for str_count (is depended upon by)

PRs and other links:

• GitHub Pull Request #10454

_{Note: This issue was originally created as ARROW-12950. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 10454
#10454