Add comprehensive LocationLink end-to-end test

- Created TestLocationLinkEndToEnd to validate full functionality
- Test uses client capabilities with LinkSupport enabled
- Verifies that cross-file go-to-definition works with LocationLink format
- Demonstrates proper integration between server, client capabilities, and definition provider

Co-authored-by: DanielRosenwasser <972891+DanielRosenwasser@users.noreply.github.com>

Author: Copilot

internal/fourslash/tests/gen/locationlink_endtoend_test.go

@@ -0,0 +1,45 @@
+package fourslash_test
+
+import (
+	"testing"
+
+	"github.com/microsoft/typescript-go/internal/fourslash"
+	"github.com/microsoft/typescript-go/internal/lsp/lsproto"
+	"github.com/microsoft/typescript-go/internal/testutil"
+)
+
+func TestLocationLinkEndToEnd(t *testing.T) {
+	t.Parallel()
+
+	defer testutil.RecoverAndFail(t, "Panic on fourslash test")
+	const content = `// @Filename: types.ts
+export interface [|/*def*/Person|] {
+    name: string;
+    age: number;
+}
+
+export function createPerson(name: string, age: number): Person {
+    return { name, age };
+}
+
+// @Filename: main.ts
+import { /*usage*/Person, createPerson } from "./types";
+
+const john: Person = createPerson("John", 30);`
+
+	// Test with LinkSupport enabled
+	linkSupport := true
+	capabilities := &lsproto.ClientCapabilities{
+		TextDocument: &lsproto.TextDocumentClientCapabilities{
+			Definition: &lsproto.DefinitionClientCapabilities{
+				LinkSupport: &linkSupport,
+			},
+		},
+	}
+
+	f := fourslash.NewFourslash(t, capabilities, content)
+	
+	// Verify that going to definition from "usage" marker works
+	// and returns LocationLink format when client supports it
+	f.VerifyBaselineGoToDefinition(t, "usage")
+}

testdata/baselines/reference/fourslash/goToDef/LocationLinkEndToEnd.baseline.jsonc

@@ -0,0 +1,15 @@
+// === goToDefinition ===
+// === /types.ts ===
+
+// export interface [|Person|] {
+//     name: string;
+//     age: number;
+// }
+// // --- (line: 5) skipped ---
+
+
+// === /main.ts ===
+
+// import { /*GO TO DEFINITION*/Person, createPerson } from "./types";
+// 
+// const john: Person = createPerson("John", 30);