R8/D8 should use sdk_version prop to determine API surface stability.

`min_sdk_version` is used to represent the api_level of the device and
its type will eventually become android.ApiLevel. OTOH,
`sdk_version` property represents the API surface a module builds against
_and_ the version of that API surface. For
R8/D8, the additional `--android-platform-build` should be determined
using the sdk_version of the soong module and not min_sdk_version, since
min_sdk_version will not contain information about the api surface used
for compilation.

The unit test for `core_platform_app` in TestR8 were passing since
min_sdk_version was not set, and therefore it implicitly defaulted to
sdk_version.

Also created a custom struct to propagate params to the helper dex
functions

Test: In build/soong, go test ./java
Test: TH
Bug: 208456999
Change-Id: I08ac6f496444d603557e498c8a1794af665abc7a

java/java.go

@@ -1981,7 +1981,15 @@ func (j *Import) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 			j.dexpreopter.uncompressedDex = *j.dexProperties.Uncompress_dex
 
 			var dexOutputFile android.OutputPath
-			dexOutputFile = j.dexer.compileDex(ctx, flags, j.MinSdkVersion(ctx), outputFile, jarName)
+			dexParams := &compileDexParams{
+				flags:         flags,
+				sdkVersion:    j.SdkVersion(ctx),
+				minSdkVersion: j.MinSdkVersion(ctx),
+				classesJar:    outputFile,
+				jarName:       jarName,
+			}
+
+			dexOutputFile = j.dexer.compileDex(ctx, dexParams)
 			if ctx.Failed() {
 				return
 			}