[Attributor] Use a pointer value type for the QueryMap

This reduces memory consumption and the need to copy complex data
structures repeatedly.

No functional change is intended.

---

Single run of the Attributor module and then CGSCC pass (oldPM)
for SPASS/clause.c (~10k LLVM-IR loc):

Before:
```
calls to allocation functions: 596180 (374484/s)
temporary memory allocations: 84979 (53378/s)
peak heap memory consumption: 52.14MB
peak RSS (including heaptrack overhead): 139.79MB
total memory leaked: 269.04KB
```

After:
```
calls to allocation functions: 489200 (303285/s)
temporary memory allocations: 83406 (51708/s)
peak heap memory consumption: 41.70MB
peak RSS (including heaptrack overhead): 131.76MB
total memory leaked: 269.04KB
```

Difference:
```
calls to allocation functions: -106980 (-5094285/s)
temporary memory allocations: -1573 (-74904/s)
peak heap memory consumption: -10.44MB
peak RSS (including heaptrack overhead): 0B
total memory leaked: 0B

---