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
Sync the mode constants used to drive vFile:open requests with these
used by GDB and defined for the gdb remote protocol. This makes it
possible to use 'platform file open' after connecting to gdbremote
server (and to some degree to operate on the open file modulo other
incompatibilities).
Differential Revision: https://reviews.llvm.org/D106985