Previously, T+ sdk snapshots used soong_config_module_type boilerplate
like for S. This change switches T+ sdk snapshots to use the
use_source_config_var property that was added in T.
Bug: 235455192
Test: atest --host mainline_modules_sdks_test
packages/modules/common/build/mainline_modules_sdks.sh
# Extract art sdk and module_exports snapshots into
# prebuilts/module_sdk/art and then run "m nothing"
Change-Id: I65cd462358bceede493623e6a51ffdb36bfc1885