Extend 'C-x 8 =' to produce characters with macron

* lisp/international/iso-transl.el (iso-transl-char-map): Add
several new sequences for characters with macron.  (Bug#55668)

etc/NEWS

@@ -203,6 +203,13 @@ files that were compiled with an old EIEIO (Emacs<25).
 ** 'C-x 8 .' has been moved to 'C-x 8 . .'.
 This is to open up the 'C-x 8 .' map to bind further characters there.
 
+---
+** 'C-x 8 =' moved to 'C-x 8 = ='.
+You can now use 'C-x 8 =' to insert several characters with macron;
+for example, 'C-x 8 = a' will insert U+0101 LATIN SMALL LETTER A WITH
+MACRON.  To insert a lone macron, type 'C-x 8 = =' instead of the
+previous 'C-x ='.
+
 ** Eshell
 
 ---

lisp/international/iso-transl.el

@@ -134,7 +134,19 @@
     ("*<"   . [?«])
     ("<"    . [?«])
     ("*="   . [?¯])
-    ("="    . [?¯])
+    ("=="   . [?¯])
+    ("=A"   . [?Ā])
+    ("=a"   . [?ā])
+    ("=E"   . [?Ē])
+    ("=e"   . [?ē])
+    ("=I"   . [?Ī])
+    ("=i"   . [?ī])
+    ("=O"   . [?Ō])
+    ("=o"   . [?ō])
+    ("=U"   . [?Ū])
+    ("=u"   . [?ū])
+    ("=Y"   . [?Ȳ])
+    ("=y"   . [?ȳ])
     ("*>"   . [?»])
     (">"    . [?»])
     ("*?"   . [?¿])