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/android/sdk_version.go b/android/sdk_version.go
index f8ac44a..18b819a 100644
--- a/android/sdk_version.go
+++ b/android/sdk_version.go
@@ -25,9 +25,9 @@
 	SdkVersion(ctx EarlyModuleContext) SdkSpec
 	// SystemModules returns the system_modules property of the current module, or an empty string if it is not set.
 	SystemModules() string
-	// MinSdkVersion returns SdkSpec that corresponds to the min_sdk_version property of the current module,
+	// MinSdkVersion returns ApiLevel that corresponds to the min_sdk_version property of the current module,
 	// or from sdk_version if it is not set.
-	MinSdkVersion(ctx EarlyModuleContext) SdkSpec
+	MinSdkVersion(ctx EarlyModuleContext) ApiLevel
 	// ReplaceMaxSdkVersionPlaceholder returns SdkSpec to replace the maxSdkVersion property of permission and
 	// uses-permission tags if it is set.
 	ReplaceMaxSdkVersionPlaceholder(ctx EarlyModuleContext) SdkSpec