[lldb-vscode] Convert launch_info and attach_info to local variables

Those fields inside of the global variable can be local variables because
they are used in only inside of one function: request_launch for launch_info
and request_attach for attach_info.

To avoid confusion an already existing local variable attach_info of
request_attach has been renamed to better reflect its purpose.

Differential Revision: https://reviews.llvm.org/D76593