Add auto deduce source map setting

Add auto deduce source map setting

    This patch adds a new "target.auto-source-map-relative" setting.

    If enabled, this setting may auto deduce a source map entry based on requested
    breakpoint path and the original path stored in debug info for resolved
    breakpoint.

    As an example, if debug info contains "./a/b/c/main.cpp", user sets a source
    breakpoint at "/root/repo/x/y/z/a/b/c/main.cpp". The breakpoint will resolve
    correctly now with Greg's patch https://reviews.llvm.org/D130401. However, the
    resolved breakpoint will use "./a/b/c/main.cpp" to locate source file during
    stop event which would fail most of the time.

    With the new "target.auto-source-map-relative" setting enabled, a auto deduced
    source map entry "." => "/root/repo/x/y/z" will be added. This new mapping will
    help lldb to map resolved breakpoint path "./a/b/c/main.cpp" back to
    "/root/repo/x/y/z/a/b/c/main.cpp" and locate it on disk.

    If an existing source map entry is used the patch also concatenates the auto
    deduced entry with any stripped reverse mapping prefix (see example below).

    As a second example, debug info contains "./a/b/c/main.cpp" and user sets
    breakpoint at "/root/repo/x/y/z/a/b/c/main.cpp". Let's say there is an existing
    source map entry "." => "/root/repo"; this mapping would strip the prefix out of
    "/root/repo/x/y/z/a/b/c/main.cpp" and use "x/y/z/a/b/c/main.cpp" to resolve
    breakpoint. "target.auto-source-map-relative" setting would auto deduce a new
    potential mapping of "." => "x/y/z", then it detects that there is a stripped
    prefix from reverse mapping and concatenates it as the new mapping:
     "." => "/root/repo/x/y/z" which would correct map "./a/b/c/main.cpp" path to
    new path in disk.

    This patches depends on https://reviews.llvm.org/D130401 to use new added
    SBDebugger::GetSetting() API for testing.

Differential Revision: https://reviews.llvm.org/D133042