Add options to skip samples (#2163)

-DFILAMENT_SKIP_SAMPLES=ON with CMake
-Pfilament_skip_samples with gradle

This change also renames CMake options specific to Filament
to avoid clashes with subprojects.

java/filamat/CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.10)
 project(filament-java)
 
-if (NOT ENABLE_JAVA)
+if (NOT FILAMENT_ENABLE_JAVA)
     return()
 endif()
 

java/filament/CMakeLists.txt

@@ -1,7 +1,7 @@
 cmake_minimum_required(VERSION 3.10)
 project(filament-java)
 
-if (NOT ENABLE_JAVA)
+if (NOT FILAMENT_ENABLE_JAVA)
     return()
 endif()