The Abstract interfaces are shared with tracing mode.
Introduce an AbstractFunction which handles the conversion between MLIR function and FunctionDef and the runtime can query whichever representation is suitable. Right now this only supports GetFunctionDef but an API for fetching the MLIR function directly will be added in future changes.
PiperOrigin-RevId: 316942774
Change-Id: I1abebbe853b98dd0048bab9fc092252f4caf3d1b