vim-patch:8.2.1289: crash when using a custom completion function (#13565)

Problem:    Crash when using a custom completion function.
Solution:   Initialize all of the expand_T. (closes vim/vim#6532)
c841afff6a

Cherry-pick CLEAR_POINTER macro from patch v8.2.0559.

N/A patches for version.c:

vim-patch:8.1.1295: when vimrun.exe does not exist external command may fail

Problem:    When vimrun.exe does not exist external command may fail.
Solution:   Use "cmd /c" twice to get the same behavior. (Ken Takata,
            closes vim/vim#4355)
98ffe4c6d8

vim-patch:8.2.2155: warning from Github actions for code analysis

Problem:    Warning from Github actions for code analysis.
Solution:   Remove the "git checkout HEAD^2" block.
18f69229c5

vim-patch:8.2.2156: Github actions run on pusing a tag

Problem:    Github actions run on pusing a tag.
Solution:   Don't run CI on tag push. Omit coveralls on pull-request.
            (Ozaki Kiichi, closes vim/vim#7489)
b5b77378bc

vim-patch:8.2.2158: CI on cirrus times out, coveralls doesn't always run

Problem:    CI on cirrus times out, coveralls doesn't always run.
Solution:   Set timeout to 20 minutes. Adjust condition. (closes vim/vim#7493)
6e562fcc07

src/nvim/vim.h

@@ -208,6 +208,7 @@ enum { FOLD_TEXT_LEN = 51 };  //!< buffer size for get_foldtext()
 // Size in bytes of the hash used in the undo file.
 #define UNDO_HASH_SIZE 32
 
+#define CLEAR_POINTER(ptr)  memset((ptr), 0, sizeof(*(ptr)))
 
 // defines to avoid typecasts from (char_u *) to (char *) and back
 // (vim_strchr() is now in strings.c)