utf8: add function to align a string into given strbuf

Add strbuf_utf8_align() which will align a given string into a strbuf
as per given align_type and width. If the width is greater than the
string length then no alignment is performed.

Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Matthieu Moy <matthieu.moy@grenoble-inp.fr>
Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

utf8.h

@@ -55,4 +55,19 @@ int mbs_chrlen(const char **text, size_t *remainder_p, const char *encoding);
  */
 int is_hfs_dotgit(const char *path);
 
+typedef enum {
+	ALIGN_LEFT,
+	ALIGN_MIDDLE,
+	ALIGN_RIGHT
+} align_type;
+
+/*
+ * Align the string given and store it into a strbuf as per the
+ * 'position' and 'width'. If the given string length is larger than
+ * 'width' than then the input string is not truncated and no
+ * alignment is done.
+ */
+void strbuf_utf8_align(struct strbuf *buf, align_type position, unsigned int width,
+		       const char *s);
+
 #endif