remove some unnecessary work

Dependencies

• [2] XUGDTYW2 stop confusingly reading a global
• [3] JY4VK7L2 rename
• [4] MXA3RZYK deduce left/right from state where possible
• [5] LERERVPH keep one screen line of overlap on pagedown
• [6] HGC5RGJP switch to line index in a function
• [7] OYXDYPGS get rid of debug variables
• [8] KURLAXXI clean up some prints
• [9] HVJKBW5U drop some unnecessary calls
• [10] NDHQN23G done passing left/right margins everywhere
• [11] UV4EWOLY add args to some functions
• [12] ODLKHO7B switch to line index in a function
• [13] M6TH7VSZ rip out notion of Line_width
• [14] 2H67P75X switch arg for a function
• [15] H2DPLWMV snapshot: wrapping long lines at word boundaries
• [16] ILOA5BYF separate data structure for each line's cache data
• [17] CBPV5SSI stop handling nil screen_line_starting_pos everywhere
• [*] BULPIBEG beginnings of a module for the text editor

Change contents

• replacement in text.lua at line 21
  [3.109]→[3.3:63](∅→∅)
  − Text.populate_screen_line_starting_pos(State, line_index)
  [2.47]

  [3.3860]
  + if line_cache.fragments == nil then

  + Text.compute_fragments(State, line_index)

  + end