vim-patch:8.2.1726: fuzzy matching only works on strings

Problem:    Fuzzy matching only works on strings.
Solution:   Support passing a dict.  Add matchfuzzypos() to also get the match
            positions. (Yegappan Lakshmanan, closes vim/vim#6947)
4f73b8e9cc

Also remove some N/A and seemingly useless NULL checks -- Nvim allocs can't
return NULL. I'm not sure why the retmatchpos stuff in match_fuzzy checks for
NULL too, given that Vim checks for NULL alloc in do_fuzzymatch; assert that the
li stuff is not NULL as that's the one check I'm ever-so-slightly unsure about.

Adjust tests. Note that the text_cb tests actually throw E6000 in Nvim, but we
also can't assert that error due to v8.2.1183 not being ported yet.

src/nvim/eval.lua

@@ -249,7 +249,8 @@ return {
     matcharg={args=1, base=1},
     matchdelete={args={1, 2}, base=1},
     matchend={args={2, 4}, base=1},
-    matchfuzzy={args=2, base=1},
+    matchfuzzy={args={2, 3}, base=1},
+    matchfuzzypos={args={2, 3}, base=1},
     matchlist={args={2, 4}, base=1},
     matchstr={args={2, 4}, base=1},
     matchstrpos={args={2,4}, base=1},