gh-139353: Rename formatter_unicode.c to unicode_formatter.c

* Move Python/formatter_unicode.c to Objects/unicode_formatter.c.
* Move Objects/stringlib/localeutil.h content into
  unicode_formatter.c. Remove localeutil.h.
* Move _PyUnicode_InsertThousandsGrouping() to unicode_formatter.c
  and mark the function as static.
* Rename unicode_fill() to _PyUnicode_Fill() and export it in
  pycore_unicodeobject.h.

Author: vstinner

Include/internal/pycore_unicodeobject.h

@@ -11,6 +11,14 @@ extern "C" {
 #include "pycore_fileutils.h"     // _Py_error_handler
 #include "pycore_ucnhash.h"       // _PyUnicode_Name_CAPI
 
+
+extern void _PyUnicode_Fill(
+    int kind,
+    void *data,
+    Py_UCS4 value,
+    Py_ssize_t start,
+    Py_ssize_t length);
+
 /* --- Characters Type APIs ----------------------------------------------- */
 
 extern int _PyUnicode_IsXidStart(Py_UCS4 ch);
@@ -240,21 +248,6 @@ extern PyObject* _PyUnicode_XStrip(
     );
 
 
-/* Using explicit passed-in values, insert the thousands grouping
-   into the string pointed to by buffer.  For the argument descriptions,
-   see Objects/stringlib/localeutil.h */
-extern Py_ssize_t _PyUnicode_InsertThousandsGrouping(
-    _PyUnicodeWriter *writer,
-    Py_ssize_t n_buffer,
-    PyObject *digits,
-    Py_ssize_t d_pos,
-    Py_ssize_t n_digits,
-    Py_ssize_t min_width,
-    const char *grouping,
-    PyObject *thousands_sep,
-    Py_UCS4 *maxchar,
-    int forward);
-
 /* Dedent a string.
    Behaviour is expected to be an exact match of `textwrap.dedent`.
    Return a new reference on success, NULL with exception set on error.

Makefile.pre.in

@@ -501,7 +501,6 @@ PYTHON_OBJS=	\
 		Python/pystrtod.o \
 		Python/pystrhex.o \
 		Python/dtoa.o \
-		Python/formatter_unicode.o \
 		Python/fileutils.o \
 		Python/suggestions.o \
 		Python/perf_trampoline.o \
@@ -558,6 +557,7 @@ OBJECT_OBJS=	\
 		Objects/tupleobject.o \
 		Objects/typeobject.o \
 		Objects/typevarobject.o \
+		Objects/unicode_formatter.o \
 		Objects/unicodeobject.o \
 		Objects/unicodectype.o \
 		Objects/unionobject.o \
@@ -2090,7 +2090,6 @@ UNICODE_DEPS = \
 		$(srcdir)/Objects/stringlib/fastsearch.h \
 		$(srcdir)/Objects/stringlib/find.h \
 		$(srcdir)/Objects/stringlib/find_max_char.h \
-		$(srcdir)/Objects/stringlib/localeutil.h \
 		$(srcdir)/Objects/stringlib/partition.h \
 		$(srcdir)/Objects/stringlib/replace.h \
 		$(srcdir)/Objects/stringlib/repr.h \