[lldb-dap] Make lldb-dap.executable-path machine specific (#137485)

Change the scope [1] of lldb-dap.executable-path to
"machine-overridable":

> Machine specific settings that can be overridden by workspace or
> folder settings.

Practically speaking, this means that the path won't be synced across
machines and "(Not synced)" will show up next to the setting. I believe
it doesn't make sense to sync this setting (and I remember a bug report
where this caused trouble when using VS Code remotely), plus it matches
what clangd does for its corresponding setting. The extension has logic
to find the binary in your path or with `xcrun` which in most cases
should do the right thing and prevent you from having to override this
setting.

[1]
https://code.visualstudio.com/api/references/contribution-points#Configuration-property-schema

Author: JDevlieghere

lldb/tools/lldb-dap/package.json

@@ -74,7 +74,8 @@
         "lldb-dap.executable-path": {
           "scope": "resource",
           "type": "string",
-          "description": "The path to the lldb-dap binary."
+          "scope": "machine-overridable",
+          "description": "The path to the lldb-dap binary, e.g. /usr/local/bin/lldb-dap"
         },
         "lldb-dap.arguments": {
           "scope": "resource",