Use CallableItem in place of MethodItem

The `MethodItem` type represents both a normal method as well as being
the super type of `ConstructorItem`. That organization causes a number
of issues in Metalava and has lead to quite a few issues where code
that only expected to be run on methods and not constructors was run on
both. So, a new type `CallableItem` has been added that will eventually
become the super type of both `MethodItem` and `ConstructorItem` and
`ConstructorItem` will no longer extend `MethodItem`.

This change prepares this code for that change by overriding
`visitCallable(CallableItem)` instead of `visitMethod(MethodItem)`
because the latter is only called for methods not constructors.

Bug: 352481366
Test: atest check-flagged-apis-test
Change-Id: I3039bc0154b00ca57cb48c7447c5901b991b57e5
diff --git a/tools/check-flagged-apis/src/com/android/checkflaggedapis/Main.kt b/tools/check-flagged-apis/src/com/android/checkflaggedapis/Main.kt
index 1125d39..d323c20 100644
--- a/tools/check-flagged-apis/src/com/android/checkflaggedapis/Main.kt
+++ b/tools/check-flagged-apis/src/com/android/checkflaggedapis/Main.kt
@@ -19,10 +19,10 @@
 
 import android.aconfig.Aconfig
 import com.android.tools.metalava.model.BaseItemVisitor
+import com.android.tools.metalava.model.CallableItem
 import com.android.tools.metalava.model.ClassItem
 import com.android.tools.metalava.model.FieldItem
 import com.android.tools.metalava.model.Item
-import com.android.tools.metalava.model.MethodItem
 import com.android.tools.metalava.model.text.ApiFile
 import com.github.ajalt.clikt.core.CliktCommand
 import com.github.ajalt.clikt.core.ProgramResult
@@ -274,15 +274,15 @@
           }
         }
 
-        override fun visitMethod(method: MethodItem) {
-          getFlagOrNull(method)?.let { flag ->
-            val methodName = buildString {
-              append(method.name())
+        override fun visitCallable(callable: CallableItem) {
+          getFlagOrNull(callable)?.let { flag ->
+            val callableSignature = buildString {
+              append(callable.name())
               append("(")
-              method.parameters().joinTo(this, separator = "") { it.type().internalName() }
+              callable.parameters().joinTo(this, separator = "") { it.type().internalName() }
               append(")")
             }
-            val symbol = Symbol.createMethod(method.containingClass().qualifiedName(), methodName)
+            val symbol = Symbol.createMethod(callable.containingClass().qualifiedName(), callableSignature)
             output.add(Pair(symbol, flag))
           }
         }