Some build system (like Buck) would normalize file paths into relative paths
in debug info to support hermetic/stable build caching.
This requires IDE/debugger users to configure correct source mapping if they
are using full path for file line breakpoint.
We are seeing many users fail to bind/resolve breakpoints due to
incorrect/missing source map.
This patch adds a new partial match setting (target.breakpoint-partial-match)
which enables matching breakpoint request by partial suffix.
The number of suffix directories required to match is controlled by another
setting (target.breakpoint-partial-match-dir-count). The default value is zero
which means matching base file name only.
This mimic what most command line lldb users/testcases are doing -- they use
base file name for setting file line breakpoint.
This setting will greatly improve breakpoint reliability in lldb-vscode useage
and can help post-mortem/off-host debugging which the file path in debug info
may not match the source location in the debug machine.