Disallow missing api source files for java_api_library module

The purpose of this change is to enable filegroups to be taken as inputs
for `java_api_library` module `api_files` property. However, since
android.MaybeExistentPathForSource() does not support this, it needs to
be replaced with android.PathForModuleSrc(), which checks for the files'
existence.

Bug: 283006953
Test: go test ./java
Change-Id: I8a7d7f200f900219cc17243194a4c26071329ee6

java/java.go

@@ -1651,7 +1651,7 @@ type JavaApiLibraryProperties struct {
 	// list of api.txt files relative to this directory that contribute to the
 	// API surface.
 	// This is a list of relative paths
-	Api_files []string
+	Api_files []string `android:"path"`
 
 	// List of flags to be passed to the javac compiler to generate jar file
 	Javacflags []string
@@ -1833,9 +1833,7 @@ func (al *ApiLibrary) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 
 	// Add the api_files inputs
 	for _, api := range al.properties.Api_files {
-		// Use MaybeExistentPathForSource since the api file might not exist during analysis.
-		// This will be provided by the orchestrator in the combined execution.
-		srcFiles = append(srcFiles, android.MaybeExistentPathForSource(ctx, ctx.ModuleDir(), api))
+		srcFiles = append(srcFiles, android.PathForModuleSrc(ctx, api))
 	}
 
 	if srcFiles == nil {