feat: add legacy beta map compatibility interfaces

[jenn-le]

Description

Adds legacy beta map compatibility interfaces for APIs that need to align with JavaScript Map while still using Fluid's map abstraction.

This change introduces FluidMapLegacy in @fluidframework/core-interfaces/legacy. It extends FluidMap and only adds the legacy/built-in Map-style members needed for compatibility: clear, delete returning boolean, set returning this, and a forEach callback typed with FluidMapLegacy.

This also adds IDirectoryBeta and ISharedMapBeta in @fluidframework/map/legacy. The existing IDirectory and ISharedMap interfaces are unchanged and continue to extend the built-in Map; the new beta variants provide an opt-in shape that consumes FluidMapLegacy.

[github-actions]

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• Security — vulnerabilities, secret exposure, injection
• API Compatibility — breaking changes, release tags, type design
• Performance — algorithmic regressions, memory leaks
• Testing — coverage gaps, hollow tests

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[Copilot]

Pull request overview

Adds new legacy/beta “Map-compatible” typing surfaces so legacy DDS APIs can align with JavaScript Map signatures while still participating in Fluid’s stable FluidMap abstraction shape.

Changes:

• Introduces FluidMapLegacy<K, V> in @fluidframework/core-interfaces (legacy/beta) to preserve Map-style mutator returns (delete(): boolean, set(): this) and clear().
• Adds IDirectoryBeta and ISharedMapBeta (legacy/beta) that replace the built-in Map inheritance with FluidMapLegacy via Omit<..., keyof Map<...>>.
• Adds compile-time type tests and updates API reports + changeset to validate/ship the new legacy surfaces.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/dds/map/src/test/types/fluidMapLegacyTypes.ts	Adds type-level assertions validating *Beta assignability to FluidMapLegacy and Map.
packages/dds/map/src/interfaces.ts	Introduces IDirectoryBeta / ISharedMapBeta using FluidMapLegacy for map-like API shape.
packages/dds/map/src/index.ts	Re-exports the new beta interfaces from the package surface (gated by @legacy @beta tags).
packages/dds/map/api-report/map.legacy.beta.api.md	Updates legacy beta API report to include the new beta interfaces.
packages/common/core-interfaces/src/test/types/fluidMapTypes.ts	Adds type-level assertions for FluidMapLegacy compatibility with FluidMap and Map.
packages/common/core-interfaces/src/index.ts	Exports FluidMapLegacy from the package index (release-tag filtered into legacy typings).
packages/common/core-interfaces/src/fluidMap.ts	Defines FluidMapLegacy<K, V> (legacy/beta) extending FluidMap with Map-style mutators.
packages/common/core-interfaces/api-report/core-interfaces.legacy.beta.api.md	Updates legacy beta API report to include FluidMapLegacy.
packages/common/core-interfaces/api-report/core-interfaces.legacy.alpha.api.md	Updates legacy alpha API report to include FluidMapLegacy (alpha rollup includes beta surfaces).
.changeset/lazy-lies-enjoy.md	Adds changeset bumping @fluidframework/core-interfaces and @fluidframework/map for the new legacy/beta types.

[github-actions]

🔗 No broken links found! ✅

Your attention to detail is admirable.

linkcheck output

> fluid-framework-docs-site@0.0.0 ci:check-links /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test "npm run serve -- --no-open" 3000 check-links

1: starting server using command "npm run serve -- --no-open"
and when url "[ 'http://127.0.0.1:3000' ]" is responding with HTTP status code 200
running tests using command "npm run check-links"


> fluid-framework-docs-site@0.0.0 serve
> docusaurus serve --no-open

[SUCCESS] Serving "build" directory at: http://localhost:3000/

> fluid-framework-docs-site@0.0.0 check-links
> linkcheck http://localhost:3000 --skip-file skipped-urls.txt

Crawling...

Stats:
  288641 links
    1922 destination URLs
    2172 URLs ignored
       0 warnings
       0 errors