Build modules from source for module products.

This overrides the branch default
(BRANCH_DEFAULT_MODULE_BUILD_FROM_SOURCE) if it is set to use
prebuilts.

Test: build/soong/soong_ui.bash --dumpvar-mode MODULE_BUILD_FROM_SOURCE
  returns false with BRANCH_DEFAULT_MODULE_BUILD_FROM_SOURCE:=false
  in internal
Test: env TARGET_PRODUCT=module_arm64 \
      build/soong/soong_ui.bash --dumpvar-mode MODULE_BUILD_FROM_SOURCE
  returns true with BRANCH_DEFAULT_MODULE_BUILD_FROM_SOURCE:=false
  in internal
Test: env TARGET_PRODUCT=mainline_modules_x86 \
      build/soong/soong_ui.bash --dumpvar-mode MODULE_BUILD_FROM_SOURCE
  returns true with BRANCH_DEFAULT_MODULE_BUILD_FROM_SOURCE:=false
  in internal
Test: env TARGET_PRODUCT=redfin \
      build/soong/soong_ui.bash --dumpvar-mode MODULE_BUILD_FROM_SOURCE
  returns false with BRANCH_DEFAULT_MODULE_BUILD_FROM_SOURCE:=false
  in internal
Bug: 222723757
Change-Id: I0faea006b0e95eff40bbfbe00cc74ba5985beeba