vim-patch:8.2.2259: Test_Executable() fails when using chroot (#13907)

Problem:    Test_Executable() fails when using chroot.
Solution:   Ignore the difference between "sbin" and "bin".
a387083b2f

Cherry-pick Test_Executable() changes from patches v8.1.1921, v8.2.1432
to be in sync with Vim.

N/A patches for version.c:

vim-patch:8.1.0509: checking cwd not accessible fails for root

Problem:    Checking cwd not accessible fails for root. (James McCoy)
Solution:   Skip this part of the test for root. (closes vim/vim#3595)
0b38f54730

vim-patch:8.2.2487: terminal shows garbage after double-wide character

Problem:    Terminal shows garbage after double-wide character with a
            combining character. (Kyoichiro Yamada)
Solution:   Libvterm: do not add the width of the combining character to the
            glyph width. (closes vim/vim#7801)
4549dad874

vim-patch:8.2.2488: json_encode() gives generic argument error

Problem:    json_encode() gives generic argument error.
Solution:   Mention the type that can't be encoded. (issue vim/vim#7802)
a853089479

src/nvim/testdir/test_functions.vim

@@ -930,10 +930,20 @@ func Test_Executable()
     " get "cat" path and remove the leading /
     let catcmd = exepath('cat')[1:]
     new
+    " check that the relative path works in /
     lcd /
     call assert_equal(1, executable(catcmd))
-    call assert_equal('/' .. catcmd, exepath(catcmd))
+    " let result = catcmd->exepath()
+    let result = exepath(catcmd)
+    " when using chroot looking for sbin/cat can return bin/cat, that is OK
+    if catcmd =~ '\<sbin\>' && result =~ '\<bin\>'
+      call assert_equal('/' .. substitute(catcmd, '\<sbin\>', 'bin', ''), result)
+    else
+      call assert_equal('/' .. catcmd, result)
+    endif
     bwipe
+  else
+    throw 'Skipped: does not work on this platform'
   endif
 endfunc