Add additional attribute support for core blocks

[ravewebdev]

Add support for remaining WP Core block attributes (e.g., text/background color, font size):

• [x] Button block: style, colors, border, width - @ravewebdev
• [x] Pullquote block: style, colors - @ravewebdev
• [x] Code block: typography - @ravewebdev
• [x] Preformatted block: typography, colors - @ravewebdev
• [x] Media & Text block: media & text settings, colors @ravewebdev
• [x] Columns block: colors, CSS class (see #470) @ravewebdev
• [x] Cover block: media settings, dimensions, overlay, CSS class (see #470) @ravewebdev
• [x] Heading block: typography, colors @ravewebdev
• [ ] Image block: styles, image settings
• [ ] Gallery block: ?
• [ ] Table block: styles, table settings, colors
• [ ] List block: typography, colors, indented inner lists do not have bullet style
• [ ] Separator: colors

Paragraph block was handled in #395 (with BE covered by BE PR #25) and can be used as an example.