fix(mappings): always include replace_keycodes in mapping dicts (#37272)

Omitting replace_keycodes when it is false causes some confusion as its
default value is unclear. In nvim_set_keymap() it defaults to false, but
in vim.keymap.set() it defaults to true when it matters.

test/functional/vimscript/map_functions_spec.lua

@@ -25,6 +25,7 @@ describe('maparg()', function()
     silent = 0,
     rhs = 'bar',
     expr = 0,
+    replace_keycodes = 0,
     sid = 0,
     scriptversion = 1,
     buffer = 0,
@@ -157,6 +158,7 @@ describe('maparg()', function()
 
         buffer = 0,
         expr = 0,
+        replace_keycodes = 0,
         mode = 'n',
         mode_bits = 0x01,
         abbr = 0,