vim-patch:8.2.4932: not easy to filter the output of maplist()

Problem:    Not easy to filter the output of maplist().
Solution:   Add mode_bits to the dictionary. (Ernie Rael, closes vim/vim#10356)

d8f5f76621

Co-authored-by: Ernie Rael <errael@raelity.com>

src/nvim/eval.lua

@@ -6195,6 +6195,11 @@ M.funcs = {
         "nowait"   Do not wait for other, longer mappings.
       	     (|:map-<nowait>|).
         "abbr"     True if this is an |abbreviation|.
+        "mode_bits" Nvim's internal binary representation of "mode".
+      	     |mapset()| ignores this; only "mode" is used.
+      	     See |maplist()| for usage examples. The values
+      	     are from src/nvim/vim.h and may change in the
+      	     future.
 
       The dictionary can be used to restore a mapping with
       |mapset()|.
@@ -6269,6 +6274,26 @@ M.funcs = {
       	echo maplist()->filter({_, m ->
       		\ match(get(m, 'rhs', ''), 'MultiMatch') >= 0
       		\ })
+      <It can be tricky to find mappings for particular |:map-modes|.
+      |mapping-dict|'s "mode_bits" can simplify this. For example,
+      the mode_bits for Normal, Insert or Command-line modes are
+      0x19. To find all the mappings available in those modes you
+      can do: >vim
+      	let saved_maps = []
+      	for m in maplist()
+      	    if and(m.mode_bits, 0x19) != 0
+      		eval saved_maps->add(m)
+      	    endif
+      	endfor
+      	echo saved_maps->mapnew({_, m -> m.lhs})
+      <The values of the mode_bits are defined in Nvim's
+      src/nvim/vim.h file and they can be discovered at runtime
+      using |:map-commands| and "maplist()". Example: >vim
+      	omap xyzzy <Nop>
+      	let op_bit = maplist()->filter(
+      	    \ {_, m -> m.lhs == 'xyzzy'})[0].mode_bits
+      	ounmap xyzzy
+      	echo printf("Operator-pending mode bit: 0x%x", op_bit)
     ]],
     name = 'maplist',
     params = {},