Rename PacManager to PacProxyInstaller

Generally, a manager class in Android is used to access
system services and it should be obtained from Context.
This class is a bit different from the definition of a
manager class.

API linter will detect an error if trying to expose a
class name end with Manager. ProxyTracker will create a
new instance of this class so this class needs to be
renamed to avoid API lint error.

Bug: 177035719
Test: FrameworksNetTests
Change-Id: I9185d4fb4342bd285a575f0bdd3518b758f37eb6

core/java/android/net/ProxyInfo.java

@@ -127,7 +127,7 @@ public class ProxyInfo implements Parcelable {
     }
 
     /**
-     * Only used in PacManager after Local Proxy is bound.
+     * Only used in PacProxyInstaller after Local Proxy is bound.
      * @hide
      */
     public ProxyInfo(@NonNull Uri pacFileUrl, int localProxyPort) {