patch 8.2.4538: the find_tags_in_file() function is too long

Problem:    The find_tags_in_file() function is too long.
Solution:   Refactor into smaller functions. (Yegappan Lakshmanan,
            closes #9920)

src/testdir/test_tagjump.vim

@@ -811,11 +811,11 @@ endfunc
 
 " Test for an unsorted tags file
 func Test_tag_sort()
-  call writefile([
+  let l = [
         \ "first\tXfoo\t1",
         \ "ten\tXfoo\t3",
-        \ "six\tXfoo\t2"],
+        \ "six\tXfoo\t2"]
-        \ 'Xtags')
+  call writefile(l, 'Xtags')
   set tags=Xtags
   let code =<< trim [CODE]
     int first() {}
@@ -826,7 +826,14 @@ func Test_tag_sort()
 
   call assert_fails('tag first', 'E432:')
 
+  " When multiple tag files are not sorted, then message should be displayed
+  " multiple times
+  call writefile(l, 'Xtags2')
+  set tags=Xtags,Xtags2
+  call assert_fails('tag first', ['E432:', 'E432:'])
+
   call delete('Xtags')
+  call delete('Xtags2')
   call delete('Xfoo')
   set tags&
   %bwipe

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4538,
 /**/
     4537,
 /**/