Add the .cppm to Doxygen

doc/Doxyfile.in

@@ -1001,48 +1001,12 @@ INPUT_FILE_ENCODING    =
 
 FILE_PATTERNS          = *.c \
                          *.cc \
-                         *.cxx \
                          *.cpp \
-                         *.c++ \
-                         *.java \
-                         *.ii \
-                         *.ixx \
                          *.ipp \
-                         *.i++ \
-                         *.inl \
-                         *.idl \
-                         *.ddl \
-                         *.odl \
                          *.h \
-                         *.hh \
-                         *.hxx \
                          *.hpp \
-                         *.h++ \
-                         *.cs \
-                         *.d \
-                         *.php \
-                         *.php4 \
-                         *.php5 \
-                         *.phtml \
-                         *.inc \
-                         *.m \
-                         *.markdown \
                          *.md \
-                         *.mm \
-                         *.dox \
-                         *.py \
-                         *.pyw \
-                         *.f90 \
-                         *.f95 \
-                         *.f03 \
-                         *.f08 \
-                         *.f \
-                         *.for \
-                         *.tcl \
-                         *.vhd \
-                         *.vhdl \
-                         *.ucf \
-                         *.qsf
+                         *.cppm \
 
 # The RECURSIVE tag can be used to specify whether or not subdirectories should
 # be searched for input files as well.