Make type narrowing of islands easier for consumers

[CMeeg]

• Consumers may need to narrow the type of a Phoria Island based on the framework in scenarios such as customising the SSR strategy in the server entry i.e. only apply a strategy if the island contains a React component
• The types for the PhoriaIsland SSR class have been amended to accept the framework name as a string literal type
• The framework plugin libraries export functions that make it convenient to check if a PhoriaIsland is using a particular framework e.g. isReactIsland
• Consumers can then use these functions to narrow the PhoriaIsland type and identify the type of framework and type of component

[changeset-bot]

🦋 Changeset detected

Latest commit: 88c9146

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 4 packages

Name	Type
@phoria/phoria	Patch
@phoria/phoria-svelte	Patch
@phoria/phoria-react	Patch
@phoria/phoria-vue	Patch

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