Send context URL as EXTRA_TEXT when available.

Also some minor test cleanups.

Bug: 242791070
Test: atest DefaultScreenshotActionsProviderTest
Flag: com.android.systemui.screenshot_context_url
Change-Id: Ieecd97fd281933207c2113905c8ad337420dfe61
diff --git a/packages/SystemUI/aconfig/systemui.aconfig b/packages/SystemUI/aconfig/systemui.aconfig
index a21a805..719ddf4 100644
--- a/packages/SystemUI/aconfig/systemui.aconfig
+++ b/packages/SystemUI/aconfig/systemui.aconfig
@@ -644,6 +644,13 @@
 }
 
 flag {
+    name: "screenshot_context_url"
+    namespace: "systemui"
+    description: "Include optional app-provided context URL when sharing a screenshot."
+    bug: "242791070"
+}
+
+flag {
    name: "run_fingerprint_detect_on_dismissible_keyguard"
    namespace: "systemui"
    description: "Run fingerprint detect instead of authenticate if the keyguard is dismissible."