feat(eval/method): partially port v8.1.1996

Problem:    More functions can be used as methods.
Solution:   Make various functions usable as a method.
aad222c9c9

Partial port as this does not include eval.txt change for listener_add.

Cherry-pick eval.txt changes for:
- bufadd from v8.1.1626:
  5ca1ac373a
- setloclist and setqflist headers from:
  b0d45e7f53

Correct eval.txt typo for settabwinvar method call (matches latest Vim).

src/nvim/eval.lua

@@ -314,18 +314,18 @@ return {
     setenv={args=2, base=2},
     setfperm={args=2, base=1},
     setline={args=2, base=2},
-    setloclist={args={2, 4}},
-    setmatches={args={1, 2}},
-    setpos={args=2},
-    setqflist={args={1, 3}},
-    setreg={args={2, 3}},
-    settabvar={args=3},
-    settabwinvar={args=4},
-    settagstack={args={2, 3}},
-    setwinvar={args=3},
-    sha256={args=1},
-    shellescape={args={1, 2}},
-    shiftwidth={args={0, 1}},
+    setloclist={args={2, 4}, base=2},
+    setmatches={args={1, 2}, base=1},
+    setpos={args=2, base=2},
+    setqflist={args={1, 3}, base=1},
+    setreg={args={2, 3}, base=2},
+    settabvar={args=3, base=3},
+    settabwinvar={args=4, base=4},
+    settagstack={args={2, 3}, base=2},
+    setwinvar={args=3, base=3},
+    sha256={args=1, base=1},
+    shellescape={args={1, 2}, base=1},
+    shiftwidth={args={0, 1}, base=1},
     sign_define={args={1, 2}, base=1},
     sign_getdefined={args={0, 1}, base=1},
     sign_getplaced={args={0, 2}, base=1},