api: Allow Uri's raw port to be the empty string.

https://datatracker.ietf.org/doc/html/rfc3986#section-3.2.3 says
  port = *DIGIT

and #section-6.2.3 explicitly lists http://example.com:/ as a valid URI.

Behavior now matches java.net.URI.

Author: jdcormie

api/src/main/java/io/grpc/Uri.java

@@ -446,9 +446,9 @@ public String getRawHost() {
     return host;
   }
 
-  /** Returns the "port" component of this URI, or -1 if not present. */
+  /** Returns the "port" component of this URI, or -1 if empty or not present. */
   public int getPort() {
-    return port != null ? Integer.parseInt(port) : -1;
+    return port != null && !port.isEmpty() ? Integer.parseInt(port) : -1;
   }
 
   /** Returns the raw port component of this URI in its originally parsed form. */
@@ -943,10 +943,12 @@ public Builder setPort(int port) {
 
     @CanIgnoreReturnValue
     Builder setRawPort(String port) {
-      try {
-        Integer.parseInt(port); // Result unused.
-      } catch (NumberFormatException e) {
-        throw new IllegalArgumentException("Invalid port", e);
+      if (port != null && !port.isEmpty()) {
+        try {
+          Integer.parseInt(port); // Result unused.
+        } catch (NumberFormatException e) {
+          throw new IllegalArgumentException("Invalid port", e);
+        }
       }
       this.port = port;
       return this;

api/src/test/java/io/grpc/UriTest.java

@@ -185,6 +185,18 @@ public void parse_emptyUserInfo() {
     assertThat(uri.toString()).isEqualTo("scheme://@host");
   }
 
+  @Test
+  public void parse_emptyPort() {
+    Uri uri = Uri.create("scheme://host:");
+    assertThat(uri.getScheme()).isEqualTo("scheme");
+    assertThat(uri.getAuthority()).isEqualTo("host:");
+    assertThat(uri.getRawAuthority()).isEqualTo("host:");
+    assertThat(uri.getHost()).isEqualTo("host");
+    assertThat(uri.getPort()).isEqualTo(-1);
+    assertThat(uri.getRawPort()).isEqualTo("");
+    assertThat(uri.toString()).isEqualTo("scheme://host:");
+  }
+
   @Test
   public void parse_invalidScheme_throws() {
     URISyntaxException e =
@@ -259,13 +271,6 @@ public void parse_invalidBackslashScope_throws() {
     assertThat(e).hasMessageThat().contains("Invalid character in scope");
   }
 
-  @Test
-  public void parse_emptyPort_throws() {
-    URISyntaxException e =
-        assertThrows(URISyntaxException.class, () -> Uri.parse("scheme://user@host:/path"));
-    assertThat(e).hasMessageThat().contains("Invalid port");
-  }
-
   @Test
   public void parse_invalidCharactersInPort_throws() {
     URISyntaxException e =