refactor: cache more observed properties

[Samillion]

Based on upstream mpv: mpv-player/mpv#17766

Changes

• Re-order local state items to match upstream mpv
• Rename state.new_file_flag to state.file_loaded to match upstream mpv
• Cache observed properties: osd-dimensions and osd-scale-by-window

Performance Difference

• Using stats.lua page 0 to compare
• We're almost the same as osc.lua with around ~1ms difference
  • modernz.lua is slower by ~1ms
  • Still not sure if this is purely due to difference in what's being rendered/tick (more elements, options and such) or something needs to be optimized.