[lldb-vscode] Add missing launchCommands entry in the package.json

[wallace]

Summary

https://reviews.llvm.org/D65363 introduced the launchCommands argument. However, it did not add
a corresponding definition in the package.json

[clayborg]

lldb/tools/lldb-vscode/package.json

145

This needs a better description that is more akin to the "attachCommands". Maybe something like:

Custom commands that are executed instead of launching a process. A target will be created with the launch arguments prior to executing these commands. The commands may optionally create a new target and must perform a launch. A valid process must exist after these commands complete or the \"launch\" will fail.

[wallace]

I pushed this by mistake, but I've just reverted the commit.

[wallace]

Use clayborg's wording. Thanks, milord.

lldb/tools/lldb-vscode/package.json

"debuggers": [
                   "description": "Initialization commands executed upon debugger startup.",
                   "default": []
               },
               "preRunCommands": {
                   "type": "array",
                   "description": "Commands executed just before the program is launched.",
                   "default": []
               },
+              "launchCommands": {
+                  "type": "array",
+                  "description": "Custom commands that are executed instead of launching a process. A target will be created with the launch arguments prior to executing these commands. The commands may optionally create a new target and must perform a launch. A valid process must exist after these commands complete or the \"launch\" will fail.",
+                  "default": []
+              },
               "stopCommands": {
                   "type": "array",
                   "description": "Commands executed each time the program stops.",
                   "default": []
               },
               "exitCommands": {
                   "type": "array",
                   "description": "Commands executed at the end of debugging session.",