Minimize cloning in swc_ecma_parser::TokenContexts

[bvanjoi]

Repeatedly cloning the vector hurts performance. We should eliminate this pattern.

[bvanjoi]

we could eliminate TokenContexts entirely and re-scan tokens on demand — similar to TypeScript's parser implementation here: https://github.com/microsoft/TypeScript/blob/main/src/compiler/parser.ts#L2223-L2241. And I will give it a try.