HackStudio: Start adding a "find in files" function

Projects now contain a set of TextDocument objects. Each TextDocument
represents a member file in the project. TextDocuments may not have
their file contents loaded at all times, but they will be loaded on
demand when calling TextDocument::contents().

"Find in files" works by iterating over the documents in the project
and calling find(needle) on each one. The return value from find() is
a vector of line numbers where the needle was found.

This is obviously going to need a bunch more work. :^)

DevTools/HackStudio/TextDocument.h

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <AK/ByteBuffer.h>
+#include <AK/NonnullRefPtr.h>
+#include <AK/RefCounted.h>
+#include <AK/String.h>
+
+class TextDocument : public RefCounted<TextDocument> {
+public:
+    static NonnullRefPtr<TextDocument> construct_with_name(const String& name)
+    {
+        return adopt(*new TextDocument(name));
+    }
+
+    const String& name() const { return m_name; }
+
+    const ByteBuffer& contents() const;
+
+    Vector<int> find(const StringView&) const;
+
+private:
+    explicit TextDocument(const String& name)
+        : m_name(name)
+    {
+    }
+
+    String m_name;
+    mutable ByteBuffer m_contents;
+};