Fix duplicate resources gradient vectors

There is currently a conflict when generating gradient vector a vector
of the same name is contained in both drawable/ and drawable folder
which has a version qualifier cooresponding to the vector type's min
supported Sdk version. E.g (icon is a gradient vector) drawable/icon.xml
and drawable-v24/icon.xml will both attempt to generate
drawable-anydpi-v24/icon.xml. This change will now check for the
existance of drawable-v24/icon.xml and avoid it from being generated
from the default drawable folder.

Bug: 164844098
Test: VectorDrawableRendererTest
Change-Id: I8b0eac5443977ec91d31bb7f86e62a6a90119347
(cherry picked from commit 5008b5dc9c61b0ba3990c175ea003f0e9b990067)
2 files changed