[lldb] Updated lldb-server to spawn the child process and share socket

`lldb-server platform --server` works on Windows now w/o multithreading. The rest functionality remains unchanged.

Fixes llvm#90923, fixes llvm#56346.

This is the part 1 of the replacement of llvm#100670.

In the part 2 I plan to switch `lldb-server gdbserver` to use `--fd` and listen a common gdb port for all gdbserver connections. Then we can remove gdb port mapping to fix llvm#97537.

Author: slydiman