Improve performance of graph-based type-checking - don't validate filepaths unnecessarily

[safesparrow]

Addresses most of the issues described in #15427 .

Change 1: speedup calculating FSharpCore dependency

We avoid calculating the same FSharpCore dependency for every file - we do it once and we avoid using filepath validation which was shown to be slow and is not necessary.

Change 2: speedup queryTrie

Do not memoize queryTrie - memoization is much more costly than the invocation itself, because it involves generating hash keys and comparing keys of type string list, and uses ConcurrentDictionary.
Also allow a dual query where two parts of the LongIdentifier as passed separately, avoiding the need to concatenate them into a new list.

This change vastly reduces the time for findDependencies calls.
Here is a DotTrace snapshot showing before:

and after:

[nojaf]

Great work!