[TIMOB-27574] Android: Replace SDK "build.properties" with gradle generated "BuildConfig" class

*Summary:* When building the Titanium SDK, we generate a "build.properties" file (similar to an INI file) providing the Titanium library's version and build time information. This file is stored under APK "assets" and is read on app startup via the Java method below. [TiApplication.loadBuildProperties()](https://github.com/appcelerator/titanium_mobile/blob/5fbe78276e04049874e13bcc0a3874593f27254e/android/titanium/src/java/org/appcelerator/titanium/TiApplication.java#L300) By default, gradle generates a BuildConfig Java class for all libraries and apps. We should use this feature instead of generating our own "build.properties" file. It will simplify our build process... and access to this info at runtime will be faster. https://developer.android.com/studio/build/gradle-tips#share-custom-fields-and-resource-values-with-your-app-code *Example:*

// The "build.gradle" file.
android {
	defaultConfig {
		buildConfigField('String', 'BUILD_VERSION', '"9.x.x"')
		buildConfigField('String', 'BUILD_TIMESTAMP', '"YYYY/MM/DD HH:MM"')
		buildConfigField('String', 'BUILD_GIT_HASH', '"HEAD"')
	}
}

*Note:* This information is logged on app startup as...

<AppName> <AppVersion> (Powered by Titanium <Version>.<GitHash>)

The above message gets logged in the code below... [ti.main.js#L15](https://github.com/appcelerator/titanium_mobile/blob/5fbe78276e04049874e13bcc0a3874593f27254e/common/Resources/ti.main.js#L15)