Handle linesStartAt1 in DAP

Handle linesStartAt1 in DAP

The DAP initialize request has a "linesStartAt1" option, where the
client can indicate that it prefers whether line numbers be 0-based or
1-based.

This patch implements this.  I audited all the line-related code in
the DAP implementation.

Note that while a similar option exists for column numbers, gdb
doesn't handle these yet, so nothing is done here.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32468