vim-patch:8.1.1823: command line history code is spread out (#19688)

Problem:    Command line history code is spread out.
Solution:   Put the code in a new file. (Yegappan Lakshmanan, closes vim/vim#4779)
            Also graduate the +cmdline_hist feature.
d7663c22c6

src/nvim/shada.c

@@ -16,11 +16,12 @@
 #include "nvim/ascii.h"
 #include "nvim/buffer.h"
 #include "nvim/buffer_defs.h"
+#include "nvim/cmdhist.h"
 #include "nvim/eval/decode.h"
 #include "nvim/eval/encode.h"
 #include "nvim/eval/typval.h"
+#include "nvim/ex_cmds.h"
 #include "nvim/ex_docmd.h"
-#include "nvim/ex_getln.h"
 #include "nvim/fileio.h"
 #include "nvim/garray.h"
 #include "nvim/globals.h"
@@ -2451,6 +2452,27 @@ static inline void find_removable_bufs(khash_t(bufset) *removable_bufs)
   }
 }
 
+/// Translate a history type number to the associated character
+static int hist_type2char(const int type)
+  FUNC_ATTR_CONST
+{
+  switch (type) {
+  case HIST_CMD:
+    return ':';
+  case HIST_SEARCH:
+    return '/';
+  case HIST_EXPR:
+    return '=';
+  case HIST_INPUT:
+    return '@';
+  case HIST_DEBUG:
+    return '>';
+  default:
+    abort();
+  }
+  return NUL;
+}
+
 /// Write ShaDa file
 ///
 /// @param[in]  sd_writer  Structure containing file writer definition.