Refactor sort_func into format_compound_unit

This is a much more logical place to put it.  Note that the default formatters (plain, html, latex) all now call `formatter` with sort_func=None so that we don't accidentally use `sorted` as a default argument.  But those who call `formatter` directly for their own purposes can call with a sort_func of their choosing that will do what they want it to do.

This also fixes a latent bug where we failed to call `sort_func` in one of the paths of `plain.py`.

Signed-off-by: Michael Tiemann <72577720+MichaelTiemannOSC@users.noreply.github.com>

pint/delegates/formatter/_format_helpers.py

@@ -265,6 +265,9 @@ def format_compound_unit(
     if locale is not None:
         out = localized_form(out, use_plural, length or "long", locale)
 
+    if registry:
+        out = registry.formatter.default_sort_func(out, registry)
+
     return out
 
 

pint/delegates/formatter/html.py

@@ -86,9 +86,7 @@ def format_unit(
             division_fmt=r"{}/{}",
             power_fmt=r"{}<sup>{}</sup>",
             parentheses_fmt=r"({})",
-            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
-                x, unit._REGISTRY
-            ),
+            sort_func=None,
         )
 
     def format_quantity(

pint/delegates/formatter/latex.py

@@ -173,8 +173,6 @@ def format_unit(
         self, unit: PlainUnit, uspec: str = "", **babel_kwds: Unpack[BabelKwds]
     ) -> str:
         units = format_compound_unit(unit, uspec, **babel_kwds)
-        # Lift the sorting by dimensions b/c the preprocessed units are unrecognizeable
-        units = unit._REGISTRY.formatter.default_sort_func(units, unit._REGISTRY)
 
         preprocessed = {rf"\mathrm{{{latex_escape(u)}}}": p for u, p in units}
         formatted = formatter(

pint/delegates/formatter/plain.py

@@ -77,6 +77,7 @@ def format_unit(
             division_fmt=" / ",
             power_fmt="{} ** {}",
             parentheses_fmt=r"({})",
+            sort_func=None,
         )
 
     def format_quantity(
@@ -175,6 +176,7 @@ def format_unit(
             division_fmt="/",
             power_fmt="{}**{}",
             parentheses_fmt=r"({})",
+            sort_func=None,
         )
 
     def format_quantity(
@@ -268,9 +270,7 @@ def format_unit(
             power_fmt="{}{}",
             parentheses_fmt="({})",
             exp_call=pretty_fmt_exponent,
-            sort_func=lambda x: unit._REGISTRY.formatter.default_sort_func(
-                x, unit._REGISTRY
-            ),
+            sort_func=None,
         )
 
     def format_quantity(