[NFC] Fix compile time regression seen on some benchmarks after a630ea30 commit

The goal of this change is fixing most of compile time slowdown seen after a630ea30 commit on lencod and sqlite3 benchmarks.
There are 3 improvements included in this patch:

1. In getNumOperands when possible get value directly from SmallNumOps.
2. Inline getLargePtr by moving its definition to header.
3. In TBAAStructTypeNode::getField get all operands once instead taking operands in loop one after one.

Differential Revision: https://reviews.llvm.org/D129468