Update min_sdk_version from SdkSpec to ApiLevel

This relands aosp/2457063. The original change broke T and U since those
branches still contain soong modules of type (kind+level). Those soong
modules have been cleaned up now

Test: Used go/abtd to test T and U branches with this change

Bug: 208456999
Change-Id: I0ef7933c055f88cb512a02108f1173e51156ef1c
diff --git a/android/api_levels.go b/android/api_levels.go
index e48a69e..0c0b2b4 100644
--- a/android/api_levels.go
+++ b/android/api_levels.go
@@ -185,6 +185,14 @@
 	return ret.String(), nil
 }
 
+// Specified returns true if the module is targeting a recognzized api_level.
+// It returns false if either
+// 1. min_sdk_version is not an int or a recognized codename
+// 2. both min_sdk_version and sdk_version are empty. In this case, MinSdkVersion() defaults to SdkSpecPrivate.ApiLevel
+func (this ApiLevel) Specified() bool {
+	return !this.IsInvalid() && !this.IsPrivate()
+}
+
 // Returns -1 if the current API level is less than the argument, 0 if they
 // are equal, and 1 if it is greater than the argument.
 func (this ApiLevel) CompareTo(other ApiLevel) int {
@@ -289,6 +297,16 @@
 	return strconv.Itoa(num)
 }
 
+// ApiLevelFrom converts the given string `raw` to an ApiLevel.
+// If `raw` is invalid (empty string, unrecognized codename etc.) it returns an invalid ApiLevel
+func ApiLevelFrom(ctx PathContext, raw string) ApiLevel {
+	ret, err := ApiLevelFromUser(ctx, raw)
+	if err != nil {
+		return NewInvalidApiLevel(raw)
+	}
+	return ret
+}
+
 // ApiLevelFromUser converts the given string `raw` to an ApiLevel, possibly returning an error.
 //
 // `raw` must be non-empty. Passing an empty string results in a panic.