Bug 1686808 - Don't use regex to parse URIs in WebExecutor. r=owlish

The harmless looking regex

```
uri.matches("(http|blob).*")
```

has a flaw: it will not accept URLs that contain a new line character. In that
case GeckoWebExecutor errors out with "Unsupported URI scheme." when in reality
that's not the problem at all.

Since it has caused a bunch of headaches to the frontend already, let's just
replace that regex with a plain `startsWith` which should work in all cases.

Differential Revision: https://phabricator.services.mozilla.com/D102943

mobile/android/geckoview/src/androidTest/java/org/mozilla/geckoview/test/WebExecutorTest.kt

@@ -445,5 +445,22 @@ class WebExecutorTest {
                         equalTo("Unsupported URI scheme: $truncated"))
             }
         }
+
+        val legal = listOf(
+            "http://$TEST_ENDPOINT\n",
+            "http://$TEST_ENDPOINT/🥲",
+            "http://$TEST_ENDPOINT/abc"
+        )
+
+        for (uri in legal) {
+            try {
+                fetch(WebRequest(uri))
+                throw IllegalStateException("fetch() should have thrown")
+            } catch (e: WebRequestError) {
+                assertThat("Request should pass initial validation.",
+                        true,
+                        equalTo(true))
+            }
+        }
     }
 }

mobile/android/geckoview/src/main/java/org/mozilla/geckoview/GeckoWebExecutor.java

@@ -141,7 +141,7 @@ public class GeckoWebExecutor {
 
         final String uri = request.uri.toLowerCase(Locale.ROOT);
         // We don't need to fully validate the URI here, just a sanity check
-        if (!uri.matches("(http|blob).*")) {
+        if (!uri.startsWith("http") && !uri.startsWith("blob")) {
             throw new IllegalArgumentException("Unsupported URI scheme: " +
                     (uri.length() > 10 ? uri.substring(0, 10) : uri));
         }