Add compatibility with AGP 4.0.1 and 4.0.2 and optimize some code

[yuruiyin]

In order to get signingConfig

• in AGP3.2+, use VariantScope.getVariantConfiguration.getSigningConfig

• in AGP4.0+, use VariantScope.getVariantDslInfo.getSigningConfig

And we don't need getBuildTypes, so we can remove getBuildTypesForAGPBefore4008() and getBuildTypesForAGP4009().

And I have verified in AGP3.5.0 ,AGP 4.0.0, AGP4.0.1, AGP4.0.2.