[RN] Add loadURLString to JitsiMeetView

Initializing a new URL/NSURL instance is a chore especially when one
takes into account that the JavaScript side (1) is loading the URL
asynchronously and (2) is capable of parsing strings that may or may not
be represented as URL/NSURL.

The Android method loadURLString(String) may have been called
loadURL(String) to overload loadURL(URL) but I didn't want to do that
because:

1. It would not be compatible with existing source code such as
loadURL(null) which would have become ambiguous.

2. I wanted to achieve better convergence with the iOS API.

android/README.md

 
 See JitsiMeetView.loadURL.
 
+#### loadURLString(String)
+
+See JitsiMeetView.loadURLString.
+
 #### setWelcomePageEnabled(boolean)
 
 See JitsiMeetView.setWelcomePageEnabled.
 
 #### loadURL(URL)
 
-Loads the given URL and joins the room. If `null` is specified, the welcome page
-is displayed instead.
+Loads a specific URL which may identify a conference to join. If the specified
+URL is null, the Welcome page is displayed instead.
+
+#### loadURLString(String)
+
+Loads a specific URL which may identify a conference to join. If the specified
+URL is null, the Welcome page is displayed instead.
 
 #### setListener(listener)
 
 Sets whether the Welcome page is enabled. See `getWelcomePageEnabled` for more
 information.
 
-NOTE: Must be called before `loadURL` for it to take effect.
+NOTE: Must be called before `loadURL`/`loadURLString` for it to take effect.
 
 #### onBackPressed()
 

android/sdk/src/main/java/org/jitsi/meet/sdk/JitsiMeetView.java

     }
 
     /**
-     * Loads the given URL and displays the conference. If the specified URL is
-     * null, the welcome page is displayed instead.
+     * Loads a specific {@link URL} which may identify a conference to join. If
+     * the specified {@code URL} is {@code null}, the Welcome page is displayed
+     * instead.
      *
-     * @param url - The conference URL.
+     * @param url - The {@code URL} to load which may identify a conference to
+     * join.
      */
     public void loadURL(@Nullable URL url) {
+        loadURLString(url == null ? null : url.toString());
+    }
+
+    /**
+     * Loads a specific URL {@link String} which may identify a conference to
+     * join. If the specified URL {@code String} is {@code null}, the Welcome
+     * page is displayed instead.
+     *
+     * @param urlString - The URL {@code String} to load which may identify a
+     * conference to join.
+     */
+    public void loadURLString(@Nullable String urlString) {
         Bundle props = new Bundle();
 
         // externalAPIScope
         props.putString("externalAPIScope", externalAPIScope);
         // url
-        if (url != null) {
-            props.putString("url", url.toString());
+        if (urlString != null) {
+            props.putString("url", urlString);
         }
         // welcomePageEnabled
         props.putBoolean("welcomePageEnabled", welcomePageEnabled);

ios/README.md

 Property for getting / setting whether the Welcome page is enabled. If NO, a
 black empty view will be rendered when not in a conference. Defaults to NO.
 
-NOTE: Must be set before calling `loadURL` for it to take effect.
+NOTE: Must be set before `loadURL:`/`loadURLString:` for it to take effect.
 
-#### loadURL(URL)
+#### loadURL:NSURL
 
 ```objc
 [meetView loadURL:[NSURL URLWithString:@"https://meet.jit.si/test123"]];
 ```
 
-Loads the given URL and joins the room. If `null` is specified, the welcome page
-is displayed instead.
+Loads a specific URL which may identify a conference to join. If the specified
+URL is `nil`, the Welcome page is displayed instead.
+
+#### loadURLString:NSString
+
+```objc
+[meetView loadURLString:@"https://meet.jit.si/test123"];
+```
+
+Loads a specific URL which may identify a conference to join. If the specified
+URL is `nil`, the Welcome page is displayed instead.
 
 #### Universal / deep linking
 

ios/sdk/src/JitsiMeetView.h

 
 - (void)loadURL:(NSURL * _Nullable)url;
 
+- (void)loadURLString:(NSString * _Nullable)urlString;
+
 @end

ios/sdk/src/JitsiMeetView.m

 #pragma mark API
 
 /**
- * Loads the given URL and joins the specified conference. If the specified URL
- * is null, the welcome page is shown.
+ * Loads a specific {@link NSURL} which may identify a conference to join. If
+ * the specified {@code NSURL} is {@code nil}, the Welcome page is displayed
+ * instead.
+ *
+ * @param url - The {@code NSURL} to load which may identify a conference to
+ * join.
  */
 - (void)loadURL:(NSURL *)url {
+    [self loadURLString:(url ? url.absoluteString : nil)];
+}
+
+/**
+ * Loads a specific URL {@link NSString} which may identify a conference to
+ * join. If the specified URL {@code NSString} is {@code nil}, the Welcome page
+ * is displayed instead.
+ *
+ * @param urlString - The URL {@code NSString} to load which may identify a
+ * conference to join.
+ */
+- (void)loadURLString:(NSString *)urlString {
     NSMutableDictionary *props = [[NSMutableDictionary alloc] init];
 
     // externalAPIScope
     [props setObject:externalAPIScope forKey:@"externalAPIScope"];
     // url
-    if (url) {
-        [props setObject:url.absoluteString forKey:@"url"];
+    if (urlString) {
+        [props setObject:urlString forKey:@"url"];
     }
     // welcomePageEnabled
     [props setObject:@(self.welcomePageEnabled) forKey:@"welcomePageEnabled"];