Rename ComponentInitializer to Initializer.

* Update unit tests.
* Update lint rules.

Test: All existing tests & lint rules pass.
Fixes: b/151873182
Change-Id: I3b5f9e0076c2acd5516333a8879aada0ac86c3d3
diff --git a/startup/startup-runtime/proguard-rules.pro b/startup/startup-runtime/proguard-rules.pro
index 8e5bea2..f55c09a 100644
--- a/startup/startup-runtime/proguard-rules.pro
+++ b/startup/startup-runtime/proguard-rules.pro
@@ -1,6 +1,6 @@
 # This Proguard rule ensures that ComponentInitializers are are neither shrunk nor obfuscated.
 # This is because they are discovered and instantiated during application initialization.
--keep class * extends androidx.startup.ComponentInitializer {
+-keep class * extends androidx.startup.Initializer {
     # Keep the public no-argument constructor while allowing other methods to be optimized.
     public <init>();
 }