LibWeb: Implement skeleton of ECDSA sign for SubtleCrypto

Author: https://github.com/stelar7
Commit: bc2a5e24bc
Pull-request: https://github.com/SerenityOS/serenity/pull/23737
Reviewed-by: https://github.com/ADKaster ✅
Reviewed-by: https://github.com/trflynn89

Tests/LibWeb/Text/input/Crypto/SubtleCrypto-sign.html

@@ -0,0 +1,32 @@
+<script src="../include.js"></script>
+<script>
+    asyncTest(async done => {
+        const encoder = new TextEncoder();
+        const message = "Hello friends";
+        const encoded_message = encoder.encode(message);
+
+        const key_algorithm = {
+            name: "ECDSA",
+            namedCurve: "P-384",
+        };
+        const extractable = true;
+        const usages = ["sign", "verify"];
+        const key = await window.crypto.subtle.generateKey(key_algorithm, extractable, usages);
+
+        const signature_algorithm = {
+            name: "ECDSA",
+            hash: { name: "SHA-384" },
+        };
+        const signature = await window.crypto.subtle.sign(
+            signature_algorithm,
+            key.privateKey,
+            encoded_message
+        );
+
+        const data_view = String.fromCharCode.apply(null, new Uint8Array(signature));
+
+        println(`Signed OK ... [${signature.byteLength} bytes total] (${data_view})`);
+
+        done();
+    });
+</script>