Add new option "libReplacement", disable by default

DRANK

Lib replacement (https://www.typescriptlang.org/docs/handbook/release-notes/typescript-4-5.html#supporting-lib-from-node_modules) allows specially-named packages in node_modules to replace TypeScript's bundled lib.d.ts files. This feature is always on, so we always perform resolution to look for it in case it exists. This can have a negative perf impact; it's extra watchers, extra CPU time, extra IO, etc. This PR adds a new compiler option libReplacement to control the feature; by default, it's disabled. This is certainly a breaking change, but I'd like to run the extended tests / perf on this to see what happens. The diff shows how much stuff we don't do when this option isn't enabled.