basename() implemented for WDL.

[DailyDreaming]

Description of WDL function to be added:

## String basename(String)

* This function returns the basename of a file path passed to it: `basename("/path/to/file.txt")` returns `"file.txt"`.
* Also supports an optional parameter, suffix to remove: `basename("/path/to/file.txt", ".txt")` returns `"file"`.https://github.com/openwdl/wdl/blob/main/versions/development/SPEC.md#string-basenamestring

• [ ] Add the following WDL function to https://github.com/DataBiosphere/toil/blob/master/src/toil/wdl/wdl_functions.py
• [ ] Add a test that runs a wdl/json with toil and then checks against cromwell to verify that toil and cromwell have the same behavior See: https://github.com/DailyDreaming/wdl-conformance-tests/tree/master/tests/standard_library

┆Issue is synchronized with this Jira Story ┆epic: WDL Standard Library Implementation ┆friendlyId: TOIL-653