(core) Generic tools for recording pycalls, deterministic mode.

Summary:
Replaces https://phab.getgrist.com/D2854

Refactoring of NSandbox:
- Simplify arguments to NSandbox.spawn. Only half the arguments were used depending on the flavour, adding a layer of confusion.
- Ensure the same environment variables are passed to both flavours of sandbox
- Simplify passing down environment variables.

Implement deterministic mode with libfaketime and a seeded random instance.
- Include static prebuilt libfaketime.so.1, may need another solution in future for other platforms.

Recording pycalls:
- Add script recordDocumentPyCalls.js to open a single document outside of tests.
- Refactor out recordPyCalls.ts to support various uses.
- Add afterEach hook to save all pycalls from server tests under $PYCALLS_DIR
- Make docTools usable without mocha.
- Add useLocalDoc and loadLocalDoc for loading non-fixture documents

Test Plan:
Made a document with formulas NOW() and UUID()
Compare two document openings in normal mode:

    diff <(test/recordDocumentPyCalls.js samples/d4W6NrzCMNVSVD6nWgNrGC.grist /dev/stdout) \
         <(test/recordDocumentPyCalls.js samples/d4W6NrzCMNVSVD6nWgNrGC.grist /dev/stdout)

Output:

    <                 1623407499.58132,
    ---
    >                 1623407499.60376,
    1195c1195
    <               "B": "bd2487f6-63c9-4f02-bbbc-5c0d674a2dc6"
    ---
    >               "B": "22e1a4fd-297f-4b86-91a2-bc42cc6da4b2"

`export DETERMINISTIC_MODE=1` and repeat. diff is empty!

Reviewers: paulfitz

Reviewed By: paulfitz

Differential Revision: https://phab.getgrist.com/D2857

app/server/declarations.d.ts

@@ -31,7 +31,7 @@ declare module "app/server/lib/shutdown" {
   export function addCleanupHandler<T>(context: T, method: (this: T) => void, timeout?: number, name?: string): void;
   export function removeCleanupHandlers<T>(context: T): void;
   export function cleanupOnSignals(...signalNames: string[]): void;
-  export function exit(optExitCode?: number): void;
+  export function exit(optExitCode?: number): Promise<void>;
 }
 
 // There is a @types/bluebird, but it's not great, and breaks for some of our usages.