Fix up the makefiles and some samples.
Fix up the makefiles and some samples.

Add LOCAL_DEX_PREOPT := false to force the samples to build actual apks.

In addition, fix a couple of other small issues:

- TtsEngine didn't have the api level set properly.
- SimpleJNI used a non-ndk library and was using libc++.

Change-Id: I1fd7c187956eed4620049bb746f4d62babcd648a

AndroidX/androidx,androidx/androidx,androidx/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,androidx/androidx,AndroidX/androidx,aosp-mirror/platform_frameworks_support,aosp-mirror/platform_frameworks_support,aosp-mirror/platform_frameworks_support,AndroidX/androidx,androidx/androidx,AndroidX/androidx,AndroidX/androidx,AndroidX/androidx,aosp-mirror/platform_frameworks_support,androidx/androidx,androidx/androidx,aosp-mirror/platform_frameworks_support,AndroidX/androidx,AndroidX/androidx,androidx/androidx,androidx/androidx