Update function-schemata sub-module to HEAD (647a2cf)

New changes:

• 47a8fb3 tests: Add direct tests for fileUtils
• ea8bf2c fileUtils: Add a file read size limit for server safety
• e91d8ec Migrate all uses of fs.readFileSync to new readFileLimited() method
• bd2d0e4 test_data/errors/canonical_Z2.yaml: Update PHP-expected errors for one case
• 14b1af8 tests: Use error.js's error constants, for coverage
• 05d9ec4 tests: Use a non-Z500 example too
• 5db8cea definitions: Add Z1229/zgh-latn ZNaturalLanguage
• 00eeb78 definitions: Change the type of Z518K2/object to be Z99/Quote
• 1654b1d When canonicalize fails, have it return Z527 error
• 647a2cf Add Z3K4: is identity as an optional field to Z3 and mark built-in identity fields.

Bug: T282716
Bug: T302519
Bug: T354917
Bug: T360496
Bug: T361260
Bug: T363390