vim-patch:8.2.4820: not simple programmatic way to find a specific mapping

Problem:    Not simple programmatic way to find a specific mapping.
Solution:   Add getmappings(). (Ernie Rael, closes vim/vim#10273)

659c240cf7

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

src/nvim/eval.lua

@@ -3957,6 +3957,22 @@ M.funcs = {
     params = { { 'nr', 'integer' }, { 'what', 'any' } },
     signature = 'getloclist({nr} [, {what}])',
   },
+  getmappings = {
+    args = 0,
+    desc = [[
+      Returns a |List| of all mappings.  Each List item is a |Dict|,
+      the same as what is returned by |maparg()|, see
+      |mapping-dict|.
+
+      Example to show all mappings with "MultiMatch" in rhs: >
+      	echo getmappings()->filter({_, m ->
+      		\ match(get(m, 'rhs', ''), 'MultiMatch') >= 0
+      		\ })
+    ]],
+    name = 'getmappings',
+    params = {},
+    signature = 'getmappings()'
+  },
   getmarklist = {
     args = { 0, 1 },
     base = 1,
@@ -6170,7 +6186,7 @@ M.funcs = {
 
       When {dict} is there and it is |TRUE| return a dictionary
       containing all the information of the mapping with the
-      following items:
+      following items:			*mapping-dict*
         "lhs"	     The {lhs} of the mapping as it would be typed
         "lhsraw"   The {lhs} of the mapping as raw bytes
         "lhsrawalt" The {lhs} of the mapping as raw bytes, alternate