fix(build): fix missing icon in the dock/dash of Linux DEs (#6303)

Author: mikelei8291

HMCL/build.gradle.kts

@@ -299,6 +299,7 @@ val makeDeb = tasks.register("makeDeb", CreateDeb::class) {
 
     version.set(project.version.toString())
     releaseType.set(debChannel)
+    launcherClassName.set("org.jackhuang.hmcl.Launcher")
     appShFile.set(layout.file(provider { artifactFile("sh") }))
     iconFile.set(layout.projectDirectory.file("image/hmcl.png"))
     outputFile.set(debFile)

buildSrc/src/main/java/org/jackhuang/hmcl/gradle/pack/CreateDeb.java

@@ -76,6 +76,10 @@ public abstract class CreateDeb extends DefaultTask {
     @Input
     public abstract Property<ReleaseType> getReleaseType();
 
+    /// Launcher class name for Linux StartupWMClass property in the .desktop file.
+    @Input
+    public abstract Property<String> getLauncherClassName();
+
     /// Executable `.sh` artifact produced by `makeExecutables`.
     @InputFile
     public abstract RegularFileProperty getAppShFile();
@@ -295,6 +299,7 @@ private String getDesktopInfo() {
                 StartupNotify=false
                 Categories=Game;
                 Keywords=mc;minecraft;
-                """.formatted(getCurrentType().getDisplayName(), getLauncherPath(), getIconTargetPath());
+                StartupWMClass=%s
+                """.formatted(getCurrentType().getDisplayName(), getLauncherPath(), getIconTargetPath(), getLauncherClassName().get());
     }
 }