LibWeb: Ignore some collapsible whitespace when building lines

When collapsing whitespace, we can skip over all-whitespace chunks at
the start of each line, and immediately following fragments that
themselves end in whitespace.

Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp

@@ -168,6 +168,10 @@ void InlineFormattingContext::generate_line_boxes(LayoutMode layout_mode)
             break;
         auto& item = item_opt.value();
 
+        // Ignore collapsible whitespace chunks at the start of line, and if the last fragment already ends in whitespace.
+        if (item.is_collapsible_whitespace && containing_block().line_boxes().last().is_empty_or_ends_in_whitespace())
+            continue;
+
         switch (item.type) {
         case InlineLevelIterator::Item::Type::ForcedBreak:
             line_builder.break_line();

Userland/Libraries/LibWeb/Layout/InlineLevelIterator.cpp

@@ -64,6 +64,7 @@ Optional<InlineLevelIterator::Item> InlineLevelIterator::next(float available_wi
             .length_in_node = chunk.length,
             .width = chunk_width,
             .should_force_break = m_text_node_context->do_respect_linebreaks && chunk.has_breaking_newline,
+            .is_collapsible_whitespace = m_text_node_context->do_collapse && chunk.is_all_whitespace,
         };
 
         return item;

Userland/Libraries/LibWeb/Layout/InlineLevelIterator.h

@@ -32,6 +32,7 @@ public:
         size_t length_in_node { 0 };
         float width { 0.0f };
         bool should_force_break { false };
+        bool is_collapsible_whitespace { false };
     };
 
     explicit InlineLevelIterator(Layout::Box& container, LayoutMode layout_mode)