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.cpp

@@ -0,0 +1,41 @@
+#include "TextDocument.h"
+#include <LibCore/CFile.h>
+#include <string.h>
+
+const ByteBuffer& TextDocument::contents() const
+{
+    if (m_contents.is_null()) {
+        auto file = CFile::construct(m_name);
+        if (file->open(CFile::ReadOnly))
+            m_contents = file->read_all();
+    }
+    return m_contents;
+}
+
+Vector<int> TextDocument::find(const StringView& needle) const
+{
+    // NOTE: This forces us to load the contents if we hadn't already.
+    contents();
+
+    Vector<int> matching_line_numbers;
+
+    String needle_as_string(needle);
+
+    int line_index = 0;
+    int start_of_line = 0;
+    for (int i = 0; i < m_contents.size(); ++i) {
+        char ch = m_contents[i];
+        if (ch == '\n') {
+            // FIXME: Please come back here and do this the good boy way.
+            String line(StringView(m_contents.data() + start_of_line, i - start_of_line));
+            auto* found = strstr(line.characters(), needle_as_string.characters());
+            if (found)
+                matching_line_numbers.append(line_index + 1);
+            ++line_index;
+            start_of_line = i + 1;
+            continue;
+        }
+    }
+
+    return matching_line_numbers;
+}