LibGUI: Update TextEditor to delete emoji based on gbp cluster

Updated TextDocument and TextEditor to use calls to
`find_grapheme_segmentation_boundary` in order to make "correct-feeling"
deletions on backspace and delete keys being pressed

Userland/Libraries/LibGUI/TextDocument.cpp

@@ -384,6 +384,34 @@ DeprecatedString TextDocument::text_in_range(TextRange const& a_range) const
     return builder.to_deprecated_string();
 }
 
+// This function will return the position of the previous grapheme cluster
+// break, relative to the cursor, for "correct looking" parsing of unicode based
+// on grapheme cluster boundary algorithm.
+size_t TextDocument::get_previous_grapheme_cluster_boundary(TextPosition const& cursor) const
+{
+    if (!cursor.is_valid())
+        return 0;
+
+    auto const& line = this->line(cursor.line());
+
+    auto index = Unicode::previous_grapheme_segmentation_boundary(line.view(), cursor.column());
+    return index.value_or(cursor.column() - 1);
+}
+
+// This function will return the position of the next grapheme cluster break,
+// relative to the cursor, for "correct looking" parsing of unicode based on
+// grapheme cluster boundary algorithm.
+size_t TextDocument::get_next_grapheme_cluster_boundary(TextPosition const& cursor) const
+{
+    if (!cursor.is_valid())
+        return 0;
+
+    auto const& line = this->line(cursor.line());
+
+    auto index = Unicode::next_grapheme_segmentation_boundary(line.view(), cursor.column());
+    return index.value_or(cursor.column() + 1);
+}
+
 u32 TextDocument::code_point_at(TextPosition const& position) const
 {
     VERIFY(position.line() < line_count());

Userland/Libraries/LibGUI/TextDocument.h

@@ -102,6 +102,9 @@ public:
     TextPosition next_position_after(TextPosition const&, SearchShouldWrap = SearchShouldWrap::Yes) const;
     TextPosition previous_position_before(TextPosition const&, SearchShouldWrap = SearchShouldWrap::Yes) const;
 
+    size_t get_next_grapheme_cluster_boundary(TextPosition const& cursor) const;
+    size_t get_previous_grapheme_cluster_boundary(TextPosition const& cursor) const;
+
     u32 code_point_at(TextPosition const&) const;
 
     TextRange range_for_entire_line(size_t line_index) const;

Userland/Libraries/LibGUI/TextEditor.cpp

@@ -961,6 +961,9 @@ void TextEditor::keydown_event(KeyEvent& event)
             if (event.modifiers() == Mod_Ctrl) {
                 auto word_break_pos = document().first_word_break_after(m_cursor);
                 erase_count = word_break_pos.column() - m_cursor.column();
+            } else {
+                auto grapheme_break_position = document().get_next_grapheme_cluster_boundary(m_cursor);
+                erase_count = grapheme_break_position - m_cursor.column();
             }
             TextRange erased_range(m_cursor, { m_cursor.line(), m_cursor.column() + erase_count });
             execute<RemoveTextCommand>(document().text_in_range(erased_range), erased_range);
@@ -1001,6 +1004,9 @@ void TextEditor::keydown_event(KeyEvent& event)
                 else
                     new_column = (m_cursor.column() / m_soft_tab_width) * m_soft_tab_width;
                 erase_count = m_cursor.column() - new_column;
+            } else {
+                auto grapheme_break_position = document().get_previous_grapheme_cluster_boundary(m_cursor);
+                erase_count = m_cursor.column() - grapheme_break_position;
             }
 
             // Backspace within line