[C++] Add better coverage for filesystem tell.

[asfimport]

Add a C++ generic file system test that writes wrote N bytes to a file. then seeks to N/2 and and read the remainder. Verify the remainder bytes are N/2 and expected from the bytes writter.

Reporter: Micah Kornfield / @emkornfield
Assignee: Ben Harkins / @benibus

PRs and other links:

• GitHub Pull Request #14064

_{Note: This issue was originally created as ARROW-16226. Please see the migration documentation for further details.}

[asfimport]

Todd Farmer / @toddfarmer:
This issue was last updated over 90 days ago, which may be an indication it is no longer being actively worked. To better reflect the current state, the issue is being unassigned per project policy. Please feel free to re-take assignment of the issue if it is being actively worked, or if you plan to start that work soon.

[asfimport]

Antoine Pitrou / @pitrou:
cc @benibus  

[asfimport]

Antoine Pitrou / @pitrou:
Issue resolved by pull request 14064
#14064