Support finding the lldb-dap binary with `xcrun` on Darwin or in PATH on
all other platforms.
Unfortunately, this PR is larger than I would like because it removes
the `lldbDapOptions`. I believe these options are not necessary, and as
previously implemented, they caused a spurious warning with this change.
The problem was that the options were created before the custom factory.
By moving the creation logic into the factory, we make sure it's only
called after the factory has been registered. The upside is that this
simplifies the code and removes a level of indirection.
ff5953804e