[lldb-vscode] Add presentation hints for scopes

Scopes can have an optional hint for how to present this scope in the UI:
https://microsoft.github.io/debug-adapter-protocol/specification#Types_Scope

The IDEs can use the hint to present the data accordingly. For example,
Visual Studio has a separate Registers window, which is populated with the
data from the scope with `presentationHint: "registers"`.

Reviewed By: wallace

Differential Revision: https://reviews.llvm.org/D113400