chore(NODE-6186): add downloading to FLE build script

[nbbeeken]

Description

What is changing?

• We now download a prebuild of libmongocrypt instead of building from source.
• --build, -b will still build from source

Is there new documentation needed for these changes?

No

What is the motivation for this change?

Now we do not need to have cmake or other toolchain requirements satisfied for libmongocrypt only what is needed for the bindings.

Double check the following

• Ran npm run check:lint script
• Self-review completed using the steps outlined here
• PR title follows the correct format: type(NODE-xxxx)[!]: description
  • Example: feat(NODE-1234)!: rewriting everything in coffeescript
• Changes are covered by tests
• New TODOs have a related JIRA ticket