vim-patch:8.2.1168: wrong method argument for appendbufline()

Problem:    Wrong method argument for appendbufline().
Solution:   Use FEARG_3.
92053ce59e

Cherry-pick base change for append (and appendbufline) from v8.2.1167.
These changes have no visible impact, but helps us sync with Vim.

Like Vim, BASE_LAST is now unused after this commit.
Keep it anyway in case it sees use in the future.
Comment-out LAST definition in eval.lua to appease linter.

src/nvim/eval.lua

@@ -17,7 +17,7 @@ end
 
 -- Usable with the base key: use the last function argument as the method base.
 -- Value is from funcs.h file. "BASE_" prefix is omitted.
-local LAST = "BASE_LAST"
+-- local LAST = "BASE_LAST" (currently unused after port of v8.2.1168)
 
 return {
   funcs={
@@ -26,8 +26,8 @@ return {
     add={args=2, base=1},
     ['and']={args=2, base=1},
     api_info={},
-    append={args=2, base=LAST},
-    appendbufline={args=3, base=LAST},
+    append={args=2, base=2},
+    appendbufline={args=3, base=3},
     argc={args={0, 1}},
     argidx={},
     arglistid={args={0, 2}},