[SYCL][Graph] Use demangled kernel name in graph node DOT output (#21496)
Add `getDemangledKernelName()` accessor to `CGExecKernel` that returns
`MDeviceKernelInfo.getDemangledName()` and use it in the graph node
`CGExecKernel` stream output so human-readable kernel names appear in
DOT graph dumps instead of mangled symbols.
Replace mangled symbol names (`_ZTS...`) in FileCheck patterns with
their demangled equivalents for Explicit and RecordReplay
debug_print_graph tests.