bugfix: never use utf8 pos in string.sub

Dependencies

• [2] I64IPGJX avoid saving fragments in lines
• [3] GZ5WULJV switch source side to new screen-line-based render
• [4] 3ZYCPNQY clearer copy
• [5] FZBXBUFF bugfix: search
• [6] 66X36NZN a little more prose describing manual_tests
• [7] HALS7E5U more clearly skip prints before screen top
• [8] KKMFQDR4 editing source code from within the app
• [9] PIEDOKYQ bugfix
• [*] BULPIBEG beginnings of a module for the text editor
• [*] BJ5X5O4A let's prevent the text cursor from ever getting on a drawing

Change contents

• replacement in text.lua at line 36
  [4.458]→[4.458:608](∅→∅)
  − if State.lines[State.cursor1.line].data:sub(State.cursor1.pos, State.cursor1.pos+utf8.len(State.search_term)-1) == State.search_term then
  [4.458]

  [2.741]
  + local data = State.lines[State.cursor1.line].data

  + local cursor_offset = Text.offset(data, State.cursor1.pos)

  + if data:sub(cursor_offset, cursor_offset+#State.search_term-1) == State.search_term then
• replacement in source_text.lua at line 58
  [4.88448]→[4.88448:88598](∅→∅)
  − if State.lines[State.cursor1.line].data:sub(State.cursor1.pos, State.cursor1.pos+utf8.len(State.search_term)-1) == State.search_term then
  [4.88448]

  [3.1540]
  + local data = State.lines[State.cursor1.line].data

  + local cursor_offset = Text.offset(data, State.cursor1.pos)

  + if data:sub(cursor_offset, cursor_offset+#State.search_term-1) == State.search_term then
• replacement in Manual_tests.md at line 31
  [4.99]→[4.99:188](∅→∅)
  − For example, `string.sub` should never use a `_pos` to substring, only an

  − `_offset`.
  [4.99]

  [4.252]
  + For example, `string.sub` should never use a `_pos`, only an `_offset`.