gen_builtin_symbols.py uses a vpython module to generate
a perfect hash function
Also seeded the perfect hash function to make it deterministic

Bug: angleproject:3747
Change-Id: I660fe71bd6b2213be9d4ccc2f68641637a49a047
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1738747
Commit-Queue: Clemen Deng <clemendeng@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>