common: Move flatpak-portal-error.[ch] back to common code

A symbol from this (flatpak_portal_error_quark) was leaked to libflatpak
due to being marked FLATPAK_EXTERN, so to keep ABI we move it back.

Fixes https://github.com/flatpak/flatpak/issues/1613

Closes: #1616
Approved by: alexlarsson

common/Makefile.am.inc

@@ -60,6 +60,8 @@ libflatpak_common_la_SOURCES = \
 	common/flatpak-table-printer.h \
 	common/flatpak-chain-input-stream.c \
 	common/flatpak-chain-input-stream.h \
+	common/flatpak-portal-error.c \
+	common/flatpak-portal-error.h \
 	common/flatpak-json.c \
 	common/flatpak-json.h \
 	common/flatpak-json-oci.c \

portal/Makefile.am.inc

@@ -28,8 +28,8 @@ flatpak_portal_SOURCES = \
 	portal/flatpak-portal.h		\
 	portal/flatpak-portal-app-info.c		\
 	portal/flatpak-portal-app-info.h		\
-	portal/flatpak-portal-error.c	\
-	portal/flatpak-portal-error.h	\
+	common/flatpak-portal-error.c	\
+	common/flatpak-portal-error.h	\
 	$(NULL)
 
 BUILT_SOURCES += $(portal_built_sources)