[lldb] [gdb-remote] Use hexadecimal numbers in vFile packats for GDB compliance

Use hexadecimal numbers rather than decimal in various vFile packets
in order to fix compatibility with gdbserver.  This also changes the few
custom LLDB packets -- while technically they do not have to be changed,
it is easier to use the same syntax consistently across LLDB.

Differential Revision: https://reviews.llvm.org/D107475