Offer extract to code behind at the start of an @code block

Without this fix, depending on where in the line the cursor is, sometimes the first code action is "Extract to Code Behind", and sometimes its "Extract to New Component". The difference is pretty jarring. Before we had "Extract to New Component", there would simply be nothing offered sometimes, but now people see the lightbulb and muscle-memory their way to the wrong action.

Author: davidwengier

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/CodeActions/Razor/ExtractToCodeBehindCodeActionProvider.cs

@@ -57,6 +57,9 @@ public Task<ImmutableArray<RazorVSInternalCodeAction>> ProvideAsync(RazorCodeAct
             // When the caret is '@$$code' or '@c$$ode' or '@co$$de' or '@cod$$e' then tree is:
             // RazorDirective -> RazorDirectiveBody -> MetaCode
             RazorDirectiveBodySyntax { Parent: RazorDirectiveSyntax d } => d,
+            // When the caret is '$$@code' then tree is:
+            // RazorDirective
+            RazorDirectiveSyntax d => d,
             _ => null
         };
         if (directiveNode is null)

src/Razor/test/Microsoft.VisualStudio.LanguageServices.Razor.Test/Cohost/CodeActions/ExtractToCodeBehindTests.cs

@@ -26,6 +26,42 @@ await VerifyCodeActionAsync(
                 <div></div>
 
 
+                """,
+            codeActionName: LanguageServerConstants.CodeActions.ExtractToCodeBehindAction,
+            additionalExpectedFiles: [
+                (FileUri("File1.razor.cs"), $$"""
+                    namespace SomeProject
+                    {
+                        public partial class File1
+                        {
+                            private int x = 1;
+                        }
+                    }
+                    """)]);
+    }
+
+    [Theory]
+    [InlineData("[||]@code {")]
+    [InlineData("@[||]code {")]
+    [InlineData("@c[||]ode {")]
+    [InlineData("@co[||]de {")]
+    [InlineData("@cod[||]e {")]
+    [InlineData("@code[||] {")]
+    [InlineData("@code[||]{")]
+    public async Task WorkAtAnyCursorPosition(string codeBlockStart)
+    {
+        await VerifyCodeActionAsync(
+            input: $$"""
+                <div></div>
+
+                {{codeBlockStart}}
+                    private int x = 1;
+                }
+                """,
+            expected: """
+                <div></div>
+
+
                 """,
             codeActionName: LanguageServerConstants.CodeActions.ExtractToCodeBehindAction,
             additionalExpectedFiles: [