Split testutils-truth into its own dependency

Rather than have testutils-ktx depend on
Truth (which pulls in Guava), move those
testutils that rely on Truth into their own
module that can be included only by the modules
that they need.

Test: ./gradlew bOS
Change-Id: I497e2b7fd4ceced3b54020647aa93da10394084a
diff --git a/settings.gradle b/settings.gradle
index 913bb2d..720685e 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -289,6 +289,7 @@
 includeProject(":internal-testutils-runtime", "testutils/testutils-runtime")
 includeProject(":internal-testutils-appcompat", "testutils/testutils-appcompat")
 includeProject(":internal-testutils-espresso", "testutils/testutils-espresso")
+includeProject(":internal-testutils-truth", "testutils/testutils-truth")
 includeProject(":internal-testutils-ktx", "testutils/testutils-ktx")
 
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