Implement sysprop_library API stability check

sysprop_library now checks the API stability itself, cutting dependency
on java_sdk_library. Under the directory {module_dir}/api,
{module_name}-current.txt and {module_name}-latest.txt hold API
signatures.

When sysprop_library is built, or a user run "m {module_name}-check-api"
command, API check is performed. First, current.txt must have exactly
same signature with built sysprop_library module. Second, current.txt
must be compatible with latest.txt.

Build system emits a handy error message to generate/update those API
files, in case of missing or mismatching. Also, a script file for
freezing API files is introduced.

Bug: 131637873
Test: 1) m && boot blueline
Test: 2) m {sysprop_library} performs API check
Test: 3) manual test for check-api, freezing api
Change-Id: I9d25f5dc64299e666527ca8e23d7233966901c4e

java/java.go

@@ -169,6 +169,10 @@ type CompilerProperties struct {
 		Output_params []string
 	}
 
+	Sysprop struct {
+		Platform *bool
+	} `blueprint:"mutated"`
+
 	Instrument bool `blueprint:"mutated"`
 
 	// List of files to include in the META-INF/services folder of the resulting jar.
@@ -999,7 +1003,6 @@ func (j *Module) collectBuilderFlags(ctx android.ModuleContext, deps deps) javaB
 }
 
 func (j *Module) compile(ctx android.ModuleContext, aaptSrcJar android.Path) {
-
 	j.exportAidlIncludeDirs = android.PathsForModuleSrc(ctx, j.deviceProperties.Aidl.Export_include_dirs)
 
 	deps := j.collectDeps(ctx)