feat(grit): implement Grit built-ins

[arendjr]

Summary

This implements all the Grit built-ins: https://docs.grit.io/language/functions#built-in-functions

Only exception for now is the log() function, which gets a bit of special treatment in the Grit engine.

Note that support for built-in functions will be important for us, as we will want to have a built-in diagnostic() function to allow for the creation of custom linter plugins.

Test Plan

Added test case. Still too low on coverage, but more is coming.

[codspeed-hq]

CodSpeed Performance Report

Merging #3987 will improve performances by 7.16%

_{Comparing arendjr:grit-built-ins (d5a75ba) with main (00760d4)}

Summary

⚡ 1 improvements
✅ 106 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	arendjr:grit-built-ins	Change
⚡	router_17129688031671448157.ts[cached]	2.2 ms	2 ms	+7.16%