[lldb] Move debug-info SDK parsing from PlatformDarwin into Platform (#144396)

Move the default `GetSDKPathFromDebugInfo` and
`ResolveSDKPathFromDebugInfo` implementations from `PlatformDarwin` into
the base `Platform` class, so non-Darwin platforms get real SDK parsing
instead of an `UnimplementedError`.

`PlatformDarwin` now only overrides the Module overload, to detect
conflicting public/internal SDKs. No functional change on Darwin.

Follow up to:
- https://github.com/llvm/llvm-project/pull/224361

rdar://171905747

GitOrigin-RevId: 3ade3984f41cbe5094e4333020e15203a93b1cb4