Simplify the TF argument mapping implementation

Use a dict to map Atest command-line arguments to a dispatch function that generates the correpsonding TF arguments. This improves readability, reduces the
number of branches, and make it easier to check if an argument is
supported.

Test: atest --host atest_unittests
Bug: b/202790364
Change-Id: I937c7e78896ffa94344f527f2d76624fa9d10aaf
1 file changed