vim-patch:8.2.0915: search() cannot skip over matches like searchpair() can

Problem:    Search() cannot skip over matches like searchpair() can.
Solution:   Add an optional "skip" argument. (Christian Brabandt, closes vim/vim#861)
adc17a5f9d

Enable skip arg usage in autoload/freebasic.vim

evalarg_T doesn't really matter because it's deleted in v8.2.0918 (and
reincarnated for Vim9 script in v8.2.1047), but I found out too late :P Anyway:

- Port evalarg_T into eval.h and use const char * and Callback fields
- Use EVALARG_INIT to initialize
- Return bool over OK/FAIL from evalarg functions
- Remove check from evalarg_clean as callback_free ignores None callbacks anyway
- Move eva_buf field into evalarg_get as a local (not sure what reason it has
  being in the struct)

N/A patches for version.c:

vim-patch:8.2.4355: unnecessary call to check_colorcolumn()

Problem:    Unnecessary call to check_colorcolumn().
Solution:   Remove the call. (Sean Dewar, closes vim/vim#9748)
0f7ff851cb

src/nvim/eval.c

@@ -3381,6 +3381,67 @@ static int eval_func(char_u **const arg, char_u *const name, const int name_len,
   return ret;
 }
 
+/// Process a function argument that can be a string expression or a function
+/// reference.
+/// "tv" must remain valid until calling evalarg_clean()!
+/// @return false when the argument is invalid.
+bool evalarg_get(typval_T *const tv, evalarg_T *const eva)
+  FUNC_ATTR_NONNULL_ALL
+{
+  if (tv->v_type == VAR_STRING || tv->v_type == VAR_NUMBER || tv->v_type == VAR_BOOL
+      || tv->v_type == VAR_SPECIAL) {
+    char numbuf[NUMBUFLEN];
+    eva->eva_string = tv_get_string_buf(tv, numbuf);
+    return true;
+  }
+
+  return callback_from_typval(&eva->eva_callback, tv);
+}
+
+/// @return whether "eva" has a valid expression or callback.
+bool evalarg_valid(const evalarg_T *const eva)
+  FUNC_ATTR_NONNULL_ALL FUNC_ATTR_CONST
+{
+  return eva->eva_string != NULL || eva->eva_callback.type != kCallbackNone;
+}
+
+/// Invoke the expression or callback "eva" and return the result in "tv".
+/// @return false if something failed
+bool evalarg_call(evalarg_T *const eva, typval_T *const tv)
+  FUNC_ATTR_NONNULL_ALL
+{
+  if (eva->eva_string != NULL) {
+    return eval0((char_u *)eva->eva_string, tv, NULL, true);
+  }
+
+  typval_T argv[1];
+  argv[0].v_type = VAR_UNKNOWN;
+  return callback_call(&eva->eva_callback, 0, argv, tv);
+}
+
+/// Like evalarg_call(), but just return true or false.
+/// Sets "error" to true if evaluation failed.
+bool evalarg_call_bool(evalarg_T *const eva, bool *const error)
+  FUNC_ATTR_NONNULL_ALL
+{
+  typval_T tv;
+  if (!evalarg_call(eva, &tv)) {
+    *error = true;
+    return false;
+  }
+
+  const bool r = tv_get_number(&tv);
+  tv_clear(&tv);
+  *error = false;
+  return r;
+}
+
+void evalarg_clean(evalarg_T *const eva)
+  FUNC_ATTR_NONNULL_ALL
+{
+  callback_free(&eva->eva_callback);
+}
+
 // TODO(ZyX-I): move to eval/expressions
 
 /*