Add test for SPKI-inside-SPKI

What if the SPKI BIT STRING contains a SPKI?  This test
aims to find out.  It is a regression test for
the code that restricts EC key encodings being lost,
as aws-lc-rs accepts an SPKI in the API we use.

src/alg_tests.rs

@@ -357,6 +357,11 @@ test_verify_signed_data!(
     "ours/ecdsa-prime256v1-sha256-compressed.pem",
     OK_IF_POINT_COMPRESSION_SUPPORTED
 );
+test_verify_signed_data!(
+    test_ecdsa_prime256v1_sha256_spki_inside_spki,
+    "ours/ecdsa-prime256v1-sha256-spki-inside-spki.pem",
+    Err(Error::InvalidSignatureForPublicKey)
+);
 
 struct TestSignedData {
     spki: Vec<u8>,

third-party/chromium/data/verify_signed_data/ours/ecdsa-prime256v1-sha256-spki-inside-spki.pem

@@ -0,0 +1,36 @@
+This is a copy of ecdsa-prime256v1-sha256.pem, but
+with the SPKI BIT STRING being the SPKI again.
+
+
+$ openssl asn1parse -i < [PUBLIC KEY]
+    0:d=0  hl=2 l= 115 cons: SEQUENCE          
+    2:d=1  hl=2 l=  19 cons:  SEQUENCE          
+    4:d=2  hl=2 l=   7 prim:   OBJECT            :id-ecPublicKey
+   13:d=2  hl=2 l=   8 prim:   OBJECT            :prime256v1
+   23:d=1  hl=2 l=  92 prim:  BIT STRING        
+
+-----BEGIN PUBLIC KEY-----
+MHMwEwYHKoZIzj0CAQYIKoZIzj0DAQcDXAAwWTATBgcqhkjOPQIBBggqhkjOPQMBBwNCAAQEqux
+zY1cm8hP7ip5k2juGMuQUlalE0ARbUi66ckD61YfZMVeYqqOlugF3V4fO0F6q97Tgn8gdbRqlRu
+g2XVJd
+-----END PUBLIC KEY-----
+
+$ openssl asn1parse -i < [ALGORITHM]
+    0:d=0  hl=2 l=  10 cons: SEQUENCE          
+    2:d=1  hl=2 l=   8 prim:  OBJECT            :ecdsa-with-SHA256
+
+-----BEGIN ALGORITHM-----
+MAoGCCqGSM49BAMC
+-----END ALGORITHM-----
+
+-----BEGIN DATA-----
+MTIzNDAw
+-----END DATA-----
+
+$ openssl asn1parse -i < [SIGNATURE]
+    0:d=0  hl=2 l=  73 prim: BIT STRING        
+
+-----BEGIN SIGNATURE-----
+A0kAMEYCIQCo6hUMuAEl1zgcTB8dqOneJxH5kXBgQGpz15BFGeUTiAIhAPOrn6aL1HlzpzstQEg
+MK6UMIsnXbsIXJXKIKTKFRJuG
+-----END SIGNATURE-----