patch 8.0.0985: libvterm has its own idea of character width

Problem:    Libvterm has its own idea of character width.
Solution:   Use the Vim functions for character width and composing to avoid a
            mismatch. (idea by Yasuhiro Matsumoto)

src/mbyte.c

@@ -1395,6 +1395,17 @@ static struct interval ambiguous[] =
     {0x100000, 0x10fffd}
 };
 
+#if defined(FEAT_TERMINAL) || defined(PROTO)
+/*
+ * utf_char2cells() with different argument type for libvterm.
+ */
+    int
+utf_uint2cells(uint32_t c)
+{
+    return utf_char2cells((int)c);
+}
+#endif
+
 /*
  * For UTF-8 character "c" return 2 for a double-width character, 1 for others.
  * Returns 4 or 6 for an unprintable character.
@@ -2296,6 +2307,17 @@ utf_char2bytes(int c, char_u *buf)
     return 6;
 }
 
+#if defined(FEAT_TERMINAL) || defined(PROTO)
+/*
+ * utf_iscomposing() with different argument type for libvterm.
+ */
+    int
+utf_iscomposing_uint(uint32_t c)
+{
+    return utf_iscomposing((int)c);
+}
+#endif
+
 /*
  * Return TRUE if "c" is a composing UTF-8 character.  This means it will be
  * drawn on top of the preceding character.