HackStudio: Highlight all the occurances of selected text in editor

This feature is similar(somewhat) to the Clion's highlight all
occurances of word under caret. This is not perfect implementation
since there is a issue with resetting the `spans` `attributes` such as
`color`, `background_color`

HackStudio: Reset spans upon mousedown_event after double clicking

Reset the spans upon mousedown_event after double clicking the text
(to highlight all occurrances). Avoid highlighting if whitespace is
selected

Userland/Libraries/LibGUI/TextEditor.cpp

@@ -248,6 +248,26 @@ TextPosition TextEditor::text_position_at(Gfx::IntPoint widget_position) const
     return text_position_at_content_position(content_position);
 }
 
+void TextEditor::highlight_all_occurances_of(DeprecatedString const selected_text)
+{
+    auto search_result = document().find_all(selected_text, false, true);
+    if (search_result.size() > 1) {
+        Vector<GUI::TextDocumentSpan> spans;
+        for (size_t i = 0; i < search_result.size(); ++i) {
+            auto& result = search_result[i];
+            GUI::TextDocumentSpan span;
+            span.range = result;
+            span.attributes.color = Color::from_argb(0xff000000);
+            span.attributes.background_color = palette().bright_yellow();
+            span.attributes.bold = true;
+            span.attributes.underline_style = Gfx::TextAttributes::UnderlineStyle::Solid;
+            spans.append(move(span));
+        }
+        document().set_spans(highlight_selected_text_span_collection_index, spans);
+        update();
+    }
+}
+
 void TextEditor::doubleclick_event(MouseEvent& event)
 {
     if (event.button() != MouseButton::Primary)
@@ -286,6 +306,10 @@ void TextEditor::doubleclick_event(MouseEvent& event)
         m_selection.set_end(document().first_word_break_after(position));
     }
 
+    auto selection = selected_text();
+    if (!selection.is_whitespace())
+        highlight_all_occurances_of(selected_text());
+
     set_cursor(m_selection.end());
     update();
     did_update_selection();
@@ -298,6 +322,7 @@ void TextEditor::mousedown_event(MouseEvent& event)
     if (event.button() != MouseButton::Primary) {
         return;
     }
+    document().set_spans(highlight_selected_text_span_collection_index, {});
 
     auto text_position = text_position_at(event.position());
     if (event.modifiers() == 0 && folding_indicator_rect(text_position.line()).contains(event.position())) {

Userland/Libraries/LibGUI/TextEditor.h

@@ -245,6 +245,7 @@ public:
         Backward,
     };
     TextRange find_text(StringView needle, SearchDirection, GUI::TextDocument::SearchShouldWrap, bool use_regex, bool match_case);
+    void highlight_all_occurances_of(DeprecatedString const selected_text);
     void reset_search_results();
     Optional<size_t> search_result_index() const { return m_search_result_index; }
     Vector<TextRange> const& search_results() const { return m_search_results; }
@@ -389,6 +390,7 @@ private:
     void on_search_results(GUI::TextRange current, Vector<GUI::TextRange> all_results);
 
     static constexpr auto search_results_span_collection_index = 1;
+    static constexpr auto highlight_selected_text_span_collection_index = 1;
 
     Type m_type { MultiLine };
     Mode m_mode { Editable };