[XLA:GPU] Move code to compute block id to tile offset indexing map to SymbolicTileAnalysis.
[XLA:GPU] Move code to compute block id to tile offset indexing map to SymbolicTileAnalysis.

The block id to tile offset map is relevant for both Triton Emitter and Cost Model, so SymbolicTileAnalysis looks like a better place to have it ATM.
