Add TARGET_RECOVERY_UI_LIB to soong_config_variable

In Android's BoardConfig, `TARGET_RECOVERY_UI_LIB` is a variable used
to specify the Recovery UI library used by the device in Recovery mode.

This `TARGET_RECOVERY_UI_LIB` is used by `librecovery_ui_ext`.
To convert `librecovery_ui_ext` to Android.bp, this variable needs to
be added to soong_config_variable for Soong to use.

Bug: 339143524
Test: m -j librecovery_ui_ext
Change-Id: I2cf01034f02e783e6bff8ce6135b9f7d1a3c62c9
diff --git a/core/android_soong_config_vars.mk b/core/android_soong_config_vars.mk
index 769a6f7..8bbf4ca 100644
--- a/core/android_soong_config_vars.mk
+++ b/core/android_soong_config_vars.mk
@@ -48,6 +48,7 @@
 RECOVERY_FSTAB_VERSION := 2
 $(call soong_config_set, recovery, recovery_api_version, $(RECOVERY_API_VERSION))
 $(call soong_config_set, recovery, recovery_fstab_version, $(RECOVERY_FSTAB_VERSION))
+$(call soong_config_set, recovery, target_recovery_ui_lib, $(TARGET_RECOVERY_UI_LIB))
 
 # For Sanitizers
 $(call soong_config_set_bool,ANDROID,ASAN_ENABLED,$(if $(filter address,$(SANITIZE_TARGET)),true,false))