simplify cursor-on-screen check

Dependencies

• [2] 5BMR5HRT click to the left of a line
• [3] HTWAM4NZ bugfix: scrolling in left/right movements
• [4] F65ADDGL add state arg to a few functions
• [5] ILOA5BYF separate data structure for each line's cache data
• [6] NHNP76LG swap return values
• [7] 2TQR4PSY add args to some functions
• [8] YJJ4X4JG bugfix: avoid scrolling on 'end'
• [9] 2L5MEZV3 experiment: new edit namespace
• [10] 62PZGSUC optimization: moving cursor to next word
• [11] MXA3RZYK deduce left/right from state where possible
• [12] LNUHQOGH start passing in Editor_state explicitly
• [13] WJBZZQE4 fold together two largely similar cases
• [14] ZPUQSPQP extract a few methods
• [15] LF7BWEG4 group all editor globals
• [16] WLJCIXYM add state arg to a few functions
• [17] TGHAJBES use line cache for drawings as well
• [18] UHB4GARJ left/right margin -> left/right coordinates
• [19] Z5HLXU4P add state arg to a few functions
• [20] QCPXQ2E3 add state arg to a few functions
• [21] KECEMMMR extract couple of functions
• [22] WOXIYUTL bugfix: manage screen_top and cursor when resizing
• [23] QCQTMUZ7 add args to some functions
• [*] BULPIBEG beginnings of a module for the text editor

Change contents

• replacement in text.lua at line 531
  [3.7909]→[3.314:362](∅→∅)
  − if Text.cursor_past_screen_bottom(State) then
  [3.7909]

  [3.1873]
  + if Text.cursor_out_of_screen(State) then
• replacement in text.lua at line 580
  [3.42]→[3.363:411](∅→∅)
  − if Text.cursor_past_screen_bottom(State) then
  [3.42]

  [3.2031]
  + if Text.cursor_out_of_screen(State) then
• replacement in text.lua at line 618
  [3.780]→[3.412:460](∅→∅)
  − if Text.cursor_past_screen_bottom(State) then
  [3.780]

  [3.2238]
  + if Text.cursor_out_of_screen(State) then
• replacement in text.lua at line 971
  [3.895]→[3.5601:5651](∅→∅)
  − if Text.cursor_past_screen_bottom(State) then
  [3.895]

  [3.956]
  + if Text.cursor_out_of_screen(State) then
• replacement in text.lua at line 982
  [3.192]→[3.865:912](∅→∅)
  − function Text.cursor_past_screen_bottom(State)
  [3.192]

  [3.234]
  + function Text.cursor_out_of_screen(State)
• replacement in text.lua at line 984
  [3.247]→[3.913:978](∅→∅)
  − return State.cursor_y >= App.screen.height - State.line_height
  [3.247]

  [3.300]
  + return State.cursor_y == nil
• replacement in edit.lua at line 137
  [2.1165]→[3.2879:2901](∅→∅),[3.2879]→[3.2879:2901](∅→∅)
  − State.cursor_y = -1
  [2.1165]

  [3.22423]
  + State.cursor_x = nil

  + State.cursor_y = nil
• edit in edit.lua at line 179
  [3.5853]→[3.5853:5859](∅→∅),[3.5859]→[3.3990:4060](∅→∅)
  − end

  − if State.cursor_y == -1 then

  − State.cursor_y = App.screen.height
• replacement in edit.lua at line 409
  [3.14227]→[3.1281:1331](∅→∅)
  − if Text.cursor_past_screen_bottom(State) then
  [3.14227]

  [3.23041]
  + if Text.cursor_out_of_screen(State) then