Restrict allowed variable symbols & reserved words

[justsml]

For all variable/token names:

• Prevent any special symbols or operators in names.
  • Opt 1: Filtering ~``!@#$%^&*()-_=+{}|[]\;:'<>?,./ - exclusionary approach can allow strange edge cases and must account for the endless strangeness of Unicode special symbols.
  • Opt 2: Must match ^[a-zA-Z0-9\.\-_]+$ - restricted can limit use cases, but much safer.
• Exclude all builtin JS functions & internal operation names.
  • parseInt, parseFloat, (there's an NPM package with arrays of this...)
  • Get a dynamic list of prefixOps and infixOps. (need to export from the expression-language/index.)
• No lone or dotted numbers (avoids some array/index collisions & weirdness.)
  • ❌ 42 = 'Antwerd'
  • ❌ 42.24 = 'Antwerd'
  • ✅ words[42] = 'Antwerd'
• Throw error on dangerous Object.prototype.... methods.
  • valueOf, toString, toJSON, etc.