Use the term "N-gon" instead of "Polygon" for triangulation method

This was reported for the Triangulate geometry node, but was also true
for the triangulate modifier and in exporters.

Note the modifier was introduced with "Ngon Method" in rBa7b44c82e5b9 but
was renamed to "Polygon Method" in rBf4762eb12ba5.

Since quads are also polygons (and quads have their own method), the
term "N-gon" is more appropriate here and is also described in the
glossary https://docs.blender.org/manual/en/2.92/glossary/
index.html#term-N-gon

Docs have been updated in rBM7539 (partially - the method would also
have to be renamed once this patch lands).

Note this also fixes the wrong enum used for the alembic exporter.

Fixes T83907

Maniphest Tasks: T83907

Differential Revision: https://developer.blender.org/D10022

source/blender/editors/mesh/editmesh_tools.c

@@ -5340,8 +5340,8 @@ void MESH_OT_quads_convert_to_tris(wmOperatorType *ot)
                "ngon_method",
                rna_enum_modifier_triangulate_ngon_method_items,
                MOD_TRIANGULATE_NGON_BEAUTY,
-               "Polygon Method",
-               "Method for splitting the polygons into triangles");
+               "N-gon Method",
+               "Method for splitting the n-gons into triangles");
 }
 
 /** \} */