chore: set max_line_length in editorconfig (#16755)

We established a while ago that 100 chars is our line length for both C
and Lua. Not all editorconfig plugins support the "max_line_length"
option, but many do (including all of the ones available for Vim/Neovim
to the best of my knowledge).

.editorconfig

@@ -8,6 +8,9 @@ end_of_line = lf
 insert_final_newline = true
 charset = utf-8
 
+[*.{c,lua}]
+max_line_length = 100
+
 [{Makefile,**/Makefile,runtime/doc/*.txt}]
 indent_style = tab
 indent_size = 8