These changes are preparing the project for a final 4.0 release:

• In tests, use "text" rather than "literal" as the type for formatted-parts text parts unicode-org/message-format-wg#1060
• Drop MessageFormat.p.resolvedOptions (What is the use case of resolvedOptions().functions ? tc39/proposal-intl-messageformat#54)
• Parametrize formatter to discriminate formatted parts (Fixes mf2 MessagePart type can't be meaningfully discriminated on type property #444)
• Use frozen null-prototype object for DefaultFunctions and DraftFunctions
• Always use a null-prototype object for MessageFormat.p.#functions
• Do not allow for literal resolution to be customized by overriding the :string function handler
• fluent: Replace getFluentFunctions with getMessageFunction
• API docs updates