* service/dap: add substitutePath configuration

Similar to substitute-path configuration in the dlv cli, substitutePath
in dap allows users to specify path mappings that are applied to the
source files in stacktrace and breakpoint requests.

Updates #2203

* service/dap: refactor the startup of the fixture for attach

Add a helper function for starting up a process to attach to.

* service/dap: update substitute path tests for windows

* service/dap: remove lines that should have been removed in merge

* respond to comments on pr

* move logging to helper functions

* make test comments more clear

* Add comments about absolute paths

* fix log messages

* clarify test comments

* remove comment about absolute paths