Update max_sdk_version from SdkSpec to ApiLevel

max_sdk_version signifies device version and does not need an sdkKind to
describe it fully. Update the type and cleanup existing usages. As a
side benefit, we also get better error handling since users can no
longer enter something like `public_30` as a valid max_sdk_version in bp
files

Bug: 208456999
Test: no change in ninja file (this should be a no-op)
Test: TH
Change-Id: I304b5ad802bde200137d8e225182828dfd6f7227
diff --git a/java/java.go b/java/java.go
index 2a7e4e1..425996a 100644
--- a/java/java.go
+++ b/java/java.go
@@ -1898,11 +1898,12 @@
 	return j.SdkVersion(ctx).ApiLevel
 }
 
-func (j *Import) ReplaceMaxSdkVersionPlaceholder(ctx android.EarlyModuleContext) android.SdkSpec {
+func (j *Import) ReplaceMaxSdkVersionPlaceholder(ctx android.EarlyModuleContext) android.ApiLevel {
 	if j.properties.Replace_max_sdk_version_placeholder != nil {
-		return android.SdkSpecFrom(ctx, *j.properties.Replace_max_sdk_version_placeholder)
+		return android.ApiLevelFrom(ctx, *j.properties.Replace_max_sdk_version_placeholder)
 	}
-	return android.SdkSpecFrom(ctx, "")
+	// Default is PrivateApiLevel
+	return android.SdkSpecPrivate.ApiLevel
 }
 
 func (j *Import) TargetSdkVersion(ctx android.EarlyModuleContext) android.ApiLevel {