test_api (cl12,cl20,cl21,cl22 - all trunks) get_kernel_arg_info "half" data type cases are missing few cases that are there in double/long cases

test_api in double/long has cases (double_scalar_d, double_vector*_d) which are not there for half data type use case. Think these cases are good to be added for half as well to improve coverage.
Example of one case for scalar_d shown below:

"kernel void half_scalar_d(half halfd,\n"
" const half consthalfd,\n"
" private half privatehalfd,\n"
" private const half privateconsthalfd)\n"
"{}\n",
"\n"

Start in the test_api coverage for get_kernel_arg_info and compare the existing double and long cases, including double_scalar_d and double_vector*_d. Add the corresponding half data type cases for the listed OpenCL trunks, then run the relevant OpenCL CTS test_api tests to confirm the coverage.

Written by the indexing model from the issue text.