Introduce Rich Text, Markdown, and Table Blocks & new Elements

[udivankin]

Introduce Rich Text, Markdown, Table, and New Elements Support

Description of Changes

This pull request significantly updates the library by integrating comprehensive support for modern Slack Block Kit features, including Rich Text, a dedicated Markdown block, the new Table block, and several new interactive elements.

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New Block Kit Components

Blocks Introduced

The following top-level block components are now supported:

• RichText (Blocks.RichText()): Used to display formatted, structured text, typically the output of Slack's WYSIWYG message composer.
• Markdown (Blocks.Markdown()): A dedicated block type for rendering Slack-flavored Markdown text.
• Table (Blocks.Table()): Allows for the display of grid data, using Rich Text sections for cell content.
  • Constraint: Table cells strictly support RichTextSection elements only.
• ContextActions (Blocks.ContextActions()): A block designed to hold related interactive elements, specifically FeedbackButtons or IconButton.

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Rich Text Composition Objects (Bits)

A full suite of composition objects for building Rich Text content is now available via the Bits namespace:

Composition Object	Builder/Accessor	Description
Rich Text Section	Bits.RichTextSection()	A container for inline rich text elements.
Rich Text List	Bits.RichTextList()	Supports bulleted (bullet) or ordered (ordered) lists.
Rich Text Quote	Bits.RichTextQuote()	For displaying quoted text.
Rich Text Preformatted	Bits.RichTextPreformatted()	For multi-line code blocks.
Rich Text Text	Bits.RichTextText()	Plain text content within a rich text container.
Rich Text Emoji	Bits.RichTextEmoji()	Inserts emoji using a name (e.g., 'wave') or Unicode value.
Rich Text Link	Bits.RichTextLink()	Inserts a hyperlink.
Rich Text User	Bits.RichTextUser()	Creates a user mention (e.g., @user).
Rich Text Channel	Bits.RichTextChannel()	Creates a channel mention (e.g., #channel).
Rich Text Usergroup	Bits.RichTextUsergroup()	Creates a usergroup mention (e.g., @usergroup).
Rich Text Broadcast	Bits.RichTextBroadcast()	Creates mentions like @here, @channel, or @everyone.
Rich Text Date	Bits.RichTextDate()	For creating formatted date/time elements.
Rich Text Color	Bits.RichTextColor()	For applying a hex color value to text.
Rich Text Team	Bits.RichTextTeam()	For mentioning a team/workspace.

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New Interactive Elements

The following interactive and contextual elements are introduced:

• RichTextInput (Elements.RichTextInput()): A dedicated input element for capturing rich, formatted text, supporting initial values and dispatch configuration.
• WorkflowButton (Elements.WorkflowButton()): A button that triggers a Slack Workflow when clicked.
• IconButton (Elements.IconButton()): A compact, icon-only button, often used in conjunction with ContextActions.
• FeedbackButtons (Elements.FeedbackButtons()): A specialized element offering positive/negative feedback buttons (e.g., "Thumbs Up"/"Thumbs Down") for the AI assistants.

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Technical Updates

• Dependency Updates: All existing internal and external references to Slack API documentation links (https://api.slack.com/) have been updated to the current standard format (https://docs.slack.dev/).
• New Constants: New enums for RichTextElementType and updated BlockType and ElementType constants were introduced to manage the new components.