[lldb-vscode] add `launchCommands` to handle launch specific commands

Authored by bulbazord on Aug 19 2019, 1:17 PM.


[lldb-vscode] add launchCommands to handle launch specific commands

This can help lldb-vscode handle launch commands associate with remote platform
attach request have field attachCommands to handle attach specific commands
add a corresponding one for launch request
if no launch command is provided, create a new target and launch; otherwise, execute the launch command

Differential Revision: https://reviews.llvm.org/D65363

Patch by Wanyi Ye <kusmour@gmail.com>

llvm-svn: 369296