Spannable-Core: Add SpannableString and ForegroundColorSpan

Spannable-Core: Add SpannableString and ForegroundColorSpan

  Create core module for Spannable
  - Interfaces: CharacterSequence, Spanned, Spannable, BaseSpan
  - Classes: SpannableString, ForegroundColorSpan, Range
  - APIs:
    - Vector<uint32_t> GetCharacters() const;
    - uint32_t GetNumberOfCharacters() const;
    - std::string ToString() const;
    - bool AttachSpan(const Dali::Toolkit::Text::BaseSpan& styleSpan, const Dali::Toolkit::Text::Range& range);
    - bool DetachSpan(const Dali::Toolkit::Text::BaseSpan& styleSpan);
    - std::vector<Dali::Toolkit::Text::BaseSpan> GetAllSpans() const;
    - void RetrieveAllSpansAndRanges(std::vector<Dali::Toolkit::Text::BaseSpan>& spans, std::vector<Dali::Toolkit::Text::Range>& ranges) const;

//Example:

    Dali::Toolkit::Text::SpannableString ss = Dali::Toolkit::Text::SpannableString::New("Hello مرحبا");

    auto chars = ss.GetCharacters();
    auto num   = ss.GetNumberOfCharacters();
    auto str   = ss.ToString();

    auto greenSpan = Dali::Toolkit::Text::ForegroundColorSpan::New(Color::GREEN);

    auto isAddedGreen = ss.AttachSpan(
      greenSpan,
      Dali::Toolkit::Text::Range::New(5u, 7u));

    auto isAddedBlue = ss.AttachSpan(
      Dali::Toolkit::Text::ForegroundColorSpan::New(Color::BLUE),
      Dali::Toolkit::Text::Range::New(4u, 2u));

    auto isAddedRed = ss.AttachSpan(
      Dali::Toolkit::Text::ForegroundColorSpan::New(Color::RED),
      Dali::Toolkit::Text::Range::New(15u, 2u));

    ss.DetachSpan(greenSpan);

    auto spans = ss.GetAllSpans();

    ss.DetachSpan(spans[0]);
    spans = ss.GetAllSpans();

Change-Id: I5e0df43d1a2e2afc8b11aa61d50e28b7e35036a4