[lldb-vscode] Make descriptive summaries and raw child for synthetics configurable (#65687)

"descriptive summaries" should only be used for small to medium binaries
because of the performance penalty the cause when completing types. I'm
defaulting it to false.
Besides that, the "raw child" for synthetics should be optional as well.
I'm defaulting it to false.

Both options can be set via a launch or attach config, following the
pattern of most settings. javascript extension wrappers can set these
settings on their own as well.