package/flutter-gallery: add a configure step

To make the next patch easier to understand, add a configure step to the
flutter-gallery.mk file. The `$(HOST_FLUTTER_SDK_BIN_FLUTTER) build bundle`
command is placed in the configure step because it generates several files
needed for the flutter_gen_snapshot tool to generate the target .so file.

Signed-off-by: Adam Duskett <adam.duskett@amarulasolutions.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/flutter-gallery/flutter-gallery.mk

@@ -14,12 +14,17 @@ FLUTTER_GALLERY_DEPENDENCIES = \
 
 FLUTTER_GALLERY_INSTALL_DIR = $(TARGET_DIR)/usr/share/flutter/gallery/$(FLUTTER_ENGINE_RUNTIME_MODE)
 
-define FLUTTER_GALLERY_BUILD_CMDS
+define FLUTTER_GALLERY_CONFIGURE_CMDS
 	cd $(@D) && \
 		FLUTTER_RUNTIME_MODES=$(FLUTTER_ENGINE_RUNTIME_MODE) \
 		$(HOST_FLUTTER_SDK_BIN_FLUTTER) clean && \
 		$(HOST_FLUTTER_SDK_BIN_FLUTTER) pub get && \
-		$(HOST_FLUTTER_SDK_BIN_FLUTTER) build bundle && \
+		$(HOST_FLUTTER_SDK_BIN_FLUTTER) build bundle
+endef
+
+define FLUTTER_GALLERY_BUILD_CMDS
+	cd $(@D) && \
+		FLUTTER_RUNTIME_MODES=$(FLUTTER_ENGINE_RUNTIME_MODE) \
 		$(HOST_FLUTTER_SDK_BIN_DART_BIN) package:gallery/main.dart && \
 		$(HOST_FLUTTER_SDK_BIN_ENV) $(FLUTTER_ENGINE_GEN_SNAPSHOT) \
 			--deterministic \