feat(dap): std source map and custom dap configuration

[arashsm79]

Add a source map for libstd; this allows stepping into the standard library source code while debugging. By setting an option in the configuration, users can choose to set up a mapping that will be used by the adapter when stepping into the standard library. Allow custom configuration to be passed to the adapter.

sourceMap launch configuration is explained in the lldb-vscode and CodeLLDB documentations.

The method used to create the source mapping

rustc --version --verbose # to find the commit hash of rustc
rustc --print sysroot     # to find the path of rust src

is described in the following references:

• Rust Discourse
• Intellij Rust
• CodeLLDB Issue

[LennyPhoenix]

+1 on this, it would be nice to not need a fork in order to change the debug adapter launch settings!