refactor(merge-tree): Use perspectives in MergeTreeTextHelper

[Abe27342]

Description

Makes IMergeTreeTextHelper take in a perspective rather than refSeq + clientId. To make this usable with the local perspective in SharedString, I've also added a localPerspective field to the collab window.

[Copilot]

Pull Request Overview

This PR refactors MergeTreeTextHelper and related components to use a unified Perspective object in place of the separate refSeq and clientId parameters. The changes update API signatures, type exports, and internal calls across the merge-tree and sharedString packages to support a local perspective for collaboration.

• Changed API for MergeTreeTextHelper#getText to accept a Perspective.
• Updated CollaborationWindow to expose a localPerspective.
• Modified tests and client/server code to use the new perspective-based approach.

Reviewed Changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/dds/merge-tree/src/mergeTreeNodes.ts	Added LocalDefaultPerspective import and initialized localPerspective in CollaborationWindow.
packages/dds/merge-tree/src/MergeTreeTextHelper.ts	Replaced separate refSeq/clientId parameters with a single Perspective parameter.
packages/dds/merge-tree/src/test/beastTest.spec.ts	Updated getText() calls to use mergeTree.localPerspective.
packages/dds/merge-tree/src/index.ts	Adjusted type exports to reflect changes in text helper interfaces.
packages/dds/merge-tree/src/test/testServer.ts	Updated perspective creation in checkTextMatchRelative calls.
packages/dds/merge-tree/src/mergeTree.ts	Changed localPerspective to a getter that retrieves data from the collabWindow.
packages/dds/merge-tree/src/textSegment.ts	Removed deprecated interface for IMergeTreeTextHelper.
packages/dds/merge-tree/src/test/mergeTree.insertingWalk.spec.ts	Updated getText() calls in test assertions.
packages/dds/merge-tree/src/test/testClient.ts	Updated getText() and relText() usage with the new perspective approach.
packages/dds/sequence/src/sharedString.ts	Updated getText() and getTextWithPlaceholders() calls to use the localPerspective.
packages/dds/merge-tree/src/client.ts	Adjusted type imports to be consistent with the refactor.
packages/dds/merge-tree/src/perspective.ts	Added @internal documentation to clarify the perspective interface.

Comments suppressed due to low confidence (1)

packages/dds/merge-tree/src/test/testClient.ts:318

• [nitpick] The use of a newly constructed PriorPerspective in relText may be inconsistent with other parts of the code that rely on mergeTree.localPerspective. Consider reviewing this call to ensure it aligns with the intended behavior for retrieving client text representations.

)} refSeq: ${refSeq}: ${this.textHelper.getText(new PriorPerspective(refSeq, clientId))}`;