Reduce PDB size for storage_grpc feature

We got
```
LINK : fatal error LNK1201: error writing to program database 'C:\b\google\cloud\storage\benchmarks\storage_throughput_vs_cpu_benchmark.pdb'; check for insufficient disk space, invalid path, or insufficient privilege
```
when building `core` feature for `storage_grpc` in `debug` mode.

We cannot use larger runner because the cost is high.

We need to research any way to reduce the PDB size of storage_grpc debug build.

Start by reproducing the `storage_grpc` `core` feature build in `debug` mode on the Windows runner and inspect the reported PDB-size failure. Research ways to reduce the debug build's PDB size without increasing runner capacity. Done means the build completes within the existing runner constraints and the approach is documented.

Written by the indexing model from the issue text.