Update min_sdk_version from SdkSpec to ApiLevel

min_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 min_sdk_version in bp
files

Will do a similar cleanup for targetSdkVersion and maxSdkVersion in a
followup CL

Test: m nothing
Test: no change in ninja files (this should be a no-op)
Bug: 208456999

Change-Id: Ie6ae7e267d093c5e4787e82685daaca1021d202e
diff --git a/java/aar.go b/java/aar.go
index 4bc5465..4e5ac1f 100644
--- a/java/aar.go
+++ b/java/aar.go
@@ -220,12 +220,12 @@
 	linkDeps = append(linkDeps, assetDeps...)
 
 	// Returns the effective version for {min|target}_sdk_version
-	effectiveVersionString := func(sdkVersion android.SdkSpec, minSdkVersion android.SdkSpec) string {
+	effectiveVersionString := func(sdkVersion android.SdkSpec, minSdkVersion android.ApiLevel) string {
 		// If {min|target}_sdk_version is current, use sdk_version to determine the effective level
 		// This is necessary for vendor modules.
 		// The effective version does not _only_ depend on {min|target}_sdk_version(level),
 		// but also on the sdk_version (kind+level)
-		if minSdkVersion.ApiLevel.IsCurrent() {
+		if minSdkVersion.IsCurrent() {
 			ret, err := sdkVersion.EffectiveVersionString(ctx)
 			if err != nil {
 				ctx.ModuleErrorf("invalid sdk_version: %s", err)
@@ -689,7 +689,7 @@
 	jniPackages android.Paths
 
 	sdkVersion    android.SdkSpec
-	minSdkVersion android.SdkSpec
+	minSdkVersion android.ApiLevel
 }
 
 var _ android.OutputFileProducer = (*AARImport)(nil)
@@ -714,11 +714,11 @@
 	return ""
 }
 
-func (a *AARImport) MinSdkVersion(ctx android.EarlyModuleContext) android.SdkSpec {
+func (a *AARImport) MinSdkVersion(ctx android.EarlyModuleContext) android.ApiLevel {
 	if a.properties.Min_sdk_version != nil {
-		return android.SdkSpecFrom(ctx, *a.properties.Min_sdk_version)
+		return android.ApiLevelFrom(ctx, *a.properties.Min_sdk_version)
 	}
-	return a.SdkVersion(ctx)
+	return a.SdkVersion(ctx).ApiLevel
 }
 
 func (a *AARImport) ReplaceMaxSdkVersionPlaceholder(ctx android.EarlyModuleContext) android.SdkSpec {