[lldb-vscode] Add inheritEnvironment option

Summary:
If no custom launching is used, lldb-vscode launches a program with an empty environment by default. In some scenarios, the user might want to simply use the same environment as the IDE to have a set of working environment variables (e.g. PATH wouldn't be empty). In fact, most DAPs in VSCode have this behavior by default. In other cases the user definitely needs to set their custom environment, which is already supported. To make the first case easier for the user (e.g. not having to copy the PATH to the launch.json every time they want to debug simple programs that rely on PATH), a new option is now offered. inheritEnvironment will launch the program copying its own environment, and it's just a boolean flag.

{F11347695}

Reviewers: clayborg, aadsm, diazhector98, kusmour

Subscribers: labath, JDevlieghere, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D74636