PhysicalFileProvider: Use active polling instead of FileSystemWatcher…

… on iOS/tvOS

In #57931 we found out that the FSEventStream APIs which are used to implement System.IO.FileSystemWatcher aren't allowed on the App Store.
According to [Apple's docs](https://developer.apple.com/documentation/coreservices/1443980-fseventstreamcreate) these APIs are only supported on macOS and Mac Catalyst.

Mark System.IO.FileSystemWatcher as unsupported on iOS/tvOS and throw PNSE.
Switch PhysicalFileProvider to use active polling instead, like we do for Browser.

Addresses #57931

src/libraries/Microsoft.Extensions.Configuration/tests/FunctionalTests/ConfigurationTests.cs

@@ -903,7 +903,7 @@ public void GetDefaultBasePathForSources()
 
         [Fact]
         [ActiveIssue("https://github.com/dotnet/runtime/issues/34582", TestPlatforms.Windows, TargetFrameworkMonikers.Netcoreapp, TestRuntimes.Mono)]
-        [SkipOnPlatform(TestPlatforms.Browser, "System.IO.FileSystem.Watcher is not supported on Browser")]
+        [SkipOnPlatform(TestPlatforms.Browser | TestPlatforms.iOS | TestPlatforms.tvOS, "System.IO.FileSystem.Watcher is not supported on Browser/iOS/tvOS")]
         public void CanEnumerateProviders()
         {
             var config = CreateBuilder()

src/libraries/Microsoft.Extensions.FileProviders.Physical/src/PhysicalFileProvider.cs

@@ -162,8 +162,8 @@ internal PhysicalFilesWatcher CreateFileWatcher()
 
             FileSystemWatcher watcher;
 #if NETCOREAPP
-            //  For browser we will proactively fallback to polling since FileSystemWatcher is not supported.
-            if (OperatingSystem.IsBrowser())
+            //  For browser/iOS/tvOS we will proactively fallback to polling since FileSystemWatcher is not supported.
+            if (OperatingSystem.IsBrowser() || (OperatingSystem.IsIOS() && !OperatingSystem.IsMacCatalyst()) || OperatingSystem.IsTvOS())
             {
                 UsePollingFileWatcher = true;
                 UseActivePolling = true;

src/libraries/Microsoft.Extensions.FileProviders.Physical/src/PhysicalFilesWatcher.cs

@@ -90,7 +90,7 @@ public PhysicalFilesWatcher(
             if (fileSystemWatcher != null)
             {
 #if NETCOREAPP
-                if (OperatingSystem.IsBrowser())
+                if (OperatingSystem.IsBrowser() || (OperatingSystem.IsIOS() && !OperatingSystem.IsMacCatalyst()) || OperatingSystem.IsTvOS())
                 {
                     throw new PlatformNotSupportedException(SR.Format(SR.FileSystemWatcher_PlatformNotSupported, typeof(FileSystemWatcher)));
                 }
@@ -148,7 +148,7 @@ public IChangeToken CreateFileChangeToken(string filter)
             }
 
             IChangeToken changeToken = GetOrAddChangeToken(filter);
-// We made sure that browser never uses FileSystemWatcher.
+// We made sure that browser/iOS/tvOS never uses FileSystemWatcher.
 #pragma warning disable CA1416 // Validate platform compatibility
             TryEnableFileSystemWatcher();
 #pragma warning restore CA1416 // Validate platform compatibility
@@ -276,6 +276,9 @@ protected virtual void Dispose(bool disposing)
         }
 
         [UnsupportedOSPlatform("browser")]
+        [UnsupportedOSPlatform("ios")]
+        [UnsupportedOSPlatform("tvos")]
+        [SupportedOSPlatform("maccatalyst")]
         private void OnRenamed(object sender, RenamedEventArgs e)
         {
             // For a file name change or a directory's name change notify registered tokens.
@@ -309,12 +312,18 @@ ex is DirectoryNotFoundException ||
         }
 
         [UnsupportedOSPlatform("browser")]
+        [UnsupportedOSPlatform("ios")]
+        [UnsupportedOSPlatform("tvos")]
+        [SupportedOSPlatform("maccatalyst")]
         private void OnChanged(object sender, FileSystemEventArgs e)
         {
             OnFileSystemEntryChange(e.FullPath);
         }
 
         [UnsupportedOSPlatform("browser")]
+        [UnsupportedOSPlatform("ios")]
+        [UnsupportedOSPlatform("tvos")]
+        [SupportedOSPlatform("maccatalyst")]
         private void OnError(object sender, ErrorEventArgs e)
         {
             // Notify all cache entries on error.
@@ -325,6 +334,9 @@ private void OnError(object sender, ErrorEventArgs e)
         }
 
         [UnsupportedOSPlatform("browser")]
+        [UnsupportedOSPlatform("ios")]
+        [UnsupportedOSPlatform("tvos")]
+        [SupportedOSPlatform("maccatalyst")]
         private void OnFileSystemEntryChange(string fullPath)
         {
             try
@@ -348,6 +360,9 @@ ex is SecurityException ||
         }
 
         [UnsupportedOSPlatform("browser")]
+        [UnsupportedOSPlatform("ios")]
+        [UnsupportedOSPlatform("tvos")]
+        [SupportedOSPlatform("maccatalyst")]
         private void ReportChangeForMatchedEntries(string path)
         {
             if (string.IsNullOrEmpty(path))
@@ -385,6 +400,9 @@ private void ReportChangeForMatchedEntries(string path)
         }
 
         [UnsupportedOSPlatform("browser")]
+        [UnsupportedOSPlatform("ios")]
+        [UnsupportedOSPlatform("tvos")]
+        [SupportedOSPlatform("maccatalyst")]
         private void TryDisableFileSystemWatcher()
         {
             if (_fileWatcher != null)
@@ -403,6 +421,9 @@ private void TryDisableFileSystemWatcher()
         }
 
         [UnsupportedOSPlatform("browser")]
+        [UnsupportedOSPlatform("ios")]
+        [UnsupportedOSPlatform("tvos")]
+        [SupportedOSPlatform("maccatalyst")]
         private void TryEnableFileSystemWatcher()
         {
             if (_fileWatcher != null)