Ref tc39/ecma262#3714
Fixes #4096

• Updates spec text to match Normative: Extend JSON.parse and JSON.stringify for interaction with the source text of primitive values ecma262#3714
• Consolidates features-independent testing of ECMAScript Standard Built-in Objects behaviors into a single builtin.js file per function, reducing clutter and improving the test262 signal-to-noise ratio.
• Improves coverage of negative zero and alternate representations of numbers and strings.
• Improves coverage of forward modification as documented in Testing plan for JSON-parse-with-source #4096.
• Adds per-test-file helper functions to improve coverage and make test intent more clear.
• Narrows assertion messages to help implementations with diagnosing test failures.
• Employs lowest-common-denominator syntax (though w.r.t. to string composition, I really am considering writing sprintf from harness/deepEqual.js: Improve formatting and align with base assert #4253 (comment) ).

Some of the tests use assert.sameValue(JSON.stringify(…), '…', …) rather than assert.deepEqual, which was a judgment call on my part that I'm happy to change if the other maintainers prefer that.