LibGfx: Reduce bit casting in OpenType CBLC table after construction

The subtables are still read at use-time for now. I'm sure we could
build some kind of wrapper structures for them though.

Userland/Libraries/LibGfx/Font/OpenType/Tables.cpp

@@ -451,12 +451,14 @@ ErrorOr<CBLC> CBLC::from_slice(ReadonlyBytes slice)
  if (slice.size() < total_size)
  return Error::from_string_literal("CBLC table too small");
 
- return CBLC { slice };
+ ReadonlySpan<BitmapSize> bitmap_sizes { bit_cast<BitmapSize const*>(slice.data() + sizeof(CblcHeader)), num_sizes };
+
+ return CBLC { slice, header, bitmap_sizes };
 }
 
 Optional<CBLC::BitmapSize const&> CBLC::bitmap_size_for_glyph_id(u32 glyph_id) const
 {
- for (auto const& bitmap_size : this->bitmap_sizes()) {
+ for (auto const& bitmap_size : m_bitmap_sizes) {
  if (glyph_id >= bitmap_size.start_glyph_index && glyph_id <= bitmap_size.end_glyph_index) {
  return bitmap_size;
  }

Userland/Libraries/LibGfx/Font/OpenType/Tables.h

@@ -549,26 +549,26 @@ class CBLC {
  BigEndian<u16> major_version;
  BigEndian<u16> minor_version;
  BigEndian<u32> num_sizes;
- BitmapSize bitmap_sizes[];
+ // Stored in a separate span:
+ // BitmapSize bitmap_sizes[];
  };
  static_assert(AssertSize<CblcHeader, 8>());
 
- CblcHeader const& header() const { return *bit_cast<CblcHeader const*>(m_slice.data()); }
- ReadonlySpan<BitmapSize> bitmap_sizes() const { return { header().bitmap_sizes, header().num_sizes }; }
- Optional<BitmapSize const&> bitmap_size_for_glyph_id(u32 glyph_id) const;
-
  static ErrorOr<CBLC> from_slice(ReadonlyBytes);
- ReadonlyBytes bytes() const { return m_slice; }
-
+ Optional<BitmapSize const&> bitmap_size_for_glyph_id(u32 glyph_id) const;
  Optional<EBLC::IndexSubHeader const&> index_subtable_for_glyph_id(u32 glyph_id, u16& first_glyph_index, u16& last_glyph_index) const;
 
 private:
- explicit CBLC(ReadonlyBytes slice)
+ explicit CBLC(ReadonlyBytes slice, CblcHeader const& header, ReadonlySpan<BitmapSize> bitmap_sizes)
  : m_slice(slice)
+ , m_header(header)
+ , m_bitmap_sizes(bitmap_sizes)
  {
  }
 
  ReadonlyBytes m_slice;
+ CblcHeader const& m_header;
+ ReadonlySpan<BitmapSize> m_bitmap_sizes;
 };
 
 // https://learn.microsoft.com/en-us/typography/opentype/spec/ebdt