Use timeTraceAsyncProfilerBegin for Source span (#83961)

This fixes incorrect trace for https://github.com/llvm/llvm-project/issues/56554.

This shows trace like

https://ui.perfetto.dev/#!/?s=aa809778dc50f2b155b062317fa18bbe2bb2fb9175e6282add8121c7c178214e
for the case shown in https://github.com/llvm/llvm-project/issues/83236.

https://github.com/llvm/llvm-project/pull/83778 is preparing PR.

Fix #56554