Add support for coverage file mapping options in a separate file

[jgebal]

To complete the mapping of utPLSQL API we need to provide ability to define file mapping options as described in documentation

The static file mapping should be optionally provided as a JSON file to the command line:

utplsql run ... -file_mappings=mappings.json

The JSON could be of following format:

{
  "source_file_mappings": [
    {
      "file_name": "sources/hr/award_bonus.prc",
      "object_owner": "HR",
      "object_name": "AWARD_BONUS",
      "object_type": "PROCEDURE"
    },
    {
      "file_name": "sources/hr/betwnstr.fnc",
      "object_owner": "HR",
      "object_name": "BETWNSTR",
      "object_type": "FUNCTION"
    }
  ],
  "test_file_mappings": [
    {
      "file_name": "test/hr/ut_award_bonus.pkb",
      "object_owner": "HR",
      "object_name": "ut_award_bonus",
      "object_type": "PACKAGE BODY"
    },
    {
      "file_name": "test/hr/ut_betwnstr.pkb",
      "object_owner": "HR",
      "object_name": "ut_betwnstr",
      "object_type": "PACKAGE BODY"
    }
  ]
}

[jgebal]

I would consider this to be of a low priority for now