Proposal: Optimize performance by dropping ast-grep

Our parsers currently use ast-grep to find definitions, which traverses the AST behind the scenes. However, we already traverse the AST when building the node and FQN maps––we could capture definitions during that existing traversal instead of doing a second one via ast-grep.

While this would require a big refactor and we'd lose ast-grep's readability benefits, it's worth noting as a potential performance optimization if we need to speed up indexing in the future.