vim-patch:8.2.0928: many type casts are used for vim_strnsave()

Problem:    Many type casts are used for vim_strnsave().
Solution:   Make the length argument size_t instead of int. (Ken Takata,
            closes vim/vim#5633)  Remove some type casts.
df44a27b53

N/A patches for version.c:

vim-patch:8.2.0315: build failure on HP-UX system

Problem:    Build failure on HP-UX system.
Solution:   Use LONG_LONG_MIN instead of LLONG_MIN.  Add type casts for switch
            statement. (John Marriott)
c593bec412

vim-patch:8.2.1052: build failure with older compilers

Problem:    Build failure with older compilers.
Solution:   Move declaration to start of block.
7acde51832

vim-patch:8.2.2229: build failure without the +eval feature

Problem:    build failure without the +eval feature.
Solution:   Add #ifdef.
39cb2dab18

vim-patch:8.2.2232: compiler error for falling through into next case

Problem:    Compiler error for falling through into next case.
Solution:   Move FALLTHROUGH below the #endif
9618a25b9c

src/nvim/eval/funcs.c

@@ -6553,7 +6553,7 @@ static void f_readfile(typval_T *argvars, typval_T *rettv, FunPtr fptr)
         }
         if (prevlen == 0) {
           assert(len < INT_MAX);
-          s = vim_strnsave(start, (int)len);
+          s = vim_strnsave(start, len);
         } else {
           /* Change "prev" buffer to be the right size.  This way
            * the bytes are only copied once, and very long lines are
@@ -10855,7 +10855,7 @@ static void f_trim(typval_T *argvars, typval_T *rettv, FunPtr fptr)
       }
     }
   }
-  rettv->vval.v_string = vim_strnsave(head, (int)(tail - head));
+  rettv->vval.v_string = vim_strnsave(head, tail - head);
 }
 
 /*

src/nvim/eval/userfunc.c

@@ -2297,9 +2297,9 @@ void ex_function(exarg_T *eap)
             // Ignore leading white space.
             p = skipwhite(p + 4);
             heredoc_trimmed =
-              vim_strnsave(theline, (int)(skipwhite(theline) - theline));
+              vim_strnsave(theline, skipwhite(theline) - theline);
           }
-          skip_until = vim_strnsave(p, (int)(skiptowhite(p) - p));
+          skip_until = vim_strnsave(p, skiptowhite(p) - p);
           do_concat = false;
           is_heredoc = true;
         }