New constant declration syntax

[feds01]

• ast: remove AccessKind differentiator
• parser: change access type and pattern syntax to use . over ::
• semantics: adjust resolution to work without AccessKind
• stdlib: update sources to use . over ::
• tests: use . over :: syntax for accessors
• ast: add is_constant flag to Declaration
• parser: support new :: constant declaration syntax
• tests: add case for constant declarations
• tests: update failed cases for new constant declaration syntax
• chore: fmt