Fix #19377 by using lookupLOcc when desugaring TH-quoted ANNs

Previously, the desugarer was looking up names referenced in TH-quoted ANNs by using globalVar, which would allocate a fresh TH Name. In effect, this would prevent quoted ANNs from ever referencing the correct identifier Name, leading to #19377 (closed). The fix is simple: instead of globalVar, use lookupLOcc, which properly looks up the name of the in-scope identifier.

Fixes #19377 (closed).