Infrastructure fixes

[kaleidawave]

• specification Immutable structure named Mutable
• Use new markdown parser in specification tests
• Use markdown parser in code blocks to script
• unflag and check tree-shaking test
• more things should be behind the number intrinsics flag
• `wasm-bindgen` version conflict resolution? #222
• Redo NaN implementation while fixing NaN implicit conversion in addition #224
• Fix mapped property test
• Fix less-than equal narrowing
  • Turns out reordering was actually turning 2 = a into a = a
• ... lots more i