The
[protocol](https://microsoft.github.io/debug-adapter-protocol//specification.html#Types_Source)
expects that `sourceReference` be less than `(2^31)-1`, but we currently
represent memory address as source reference, this can be truncated
either when sending through json or by the client. Instead, generate new
source references based on the memory address.
Make the `ResolveSource` function return an optional source.
Refactor code revolving source objects such that most logics will be
reused.
The main change is to expose a single `CreateSource(addr, target)` that
can return either a normal or an assembly source object, and call
`ShouldDisplayAssemblySource()` only from this function instead of
multiple places across the code.
Other functions can use `source.IsAssemblySource()` in order to check
which type the source is.
Replace Get{Signed,Unsigned} with GetInteger<T> and return std::optional
so you can distinguish between the value not being present and it being
explicitly set to the previous fail_value. All existing uses are
replaced by calling value_or(fail_value).
Continuation of #129818
