Add gbenchmark for strings find/contains functions

[davidwendt]

Reference #5698
This creates a gbenchmark for the cudf::strings::contains, cudf::strings::find, cudf::strings::find_multiple, cudf::strings::starts_with, and cudf::strings::ends_with.

This also includes some improvements for starts_with and ends_with to use string_view::compare instead of string_view::find since compare would be more efficient when checking for a string at a specific position. This improved the performance of these two functions by 2-3x on average.

[kkraus14]

cmake lgtm

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (branch-0.19@7a6e60e). Click here to learn what that means.
The diff coverage is n/a.

@@              Coverage Diff               @@
##             branch-0.19    #7392   +/-   ##
==============================================
  Coverage               ?   81.80%           
==============================================
  Files                  ?      101           
  Lines                  ?    16695           
  Branches               ?        0           
==============================================
  Hits                   ?    13658           
  Misses                 ?     3037           
  Partials               ?        0           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 7a6e60e...be4d0f6. Read the comment docs.

[kkraus14]

@gpucibot merge