[lldb] Updated lldb-server to spawn the child process and share socket (llvm#101283)

`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 fiх llvm#97537.

Author: slydiman