[visitor-plugin-common] fix: declare masked fragment types for unselected union members

[Tyagiquamar]

Description

A fragment on a union or interface was dropping member types that selected no fields. With inlineFragmentTypes set to mask or combine, a nested spread still referred to those per-member names, so the generated TypeScript did not compile (Cannot find name).

SelectionSetToObject now keeps one type per member in that case. A member with no selected fields is Record<PropertyKey, never>. The exported fragment type is the union of those members, which is the same shape already used when every member has a selection.

Related #10920

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

A masked or combined fragment that previously collapsed to only the selected union member is now a union that includes an empty type for each unselected member. That matches the names nested spreads already generated.

How Has This Been Tested?

• pnpm exec prettier --check on selection-set-to-object.ts, ts-documents.spec.ts, and the changeset. Result: all matched files use Prettier code style.
• pnpm exec vitest --no-watch packages/plugins/typescript/operations/tests/ts-documents.spec.ts in node:24-bookworm with pnpm 11.24.0. Result: 114 passed, including the new #10920 case, which typechecks the generated output.
• pnpm exec eslint packages/plugins/other/visitor-plugin-common/src/selection-set-to-object.ts on the host after an offline install. Result: exit 0.

Test Environment:

• OS: Linux (Docker node:24-bookworm) for Prettier and Vitest; Windows for ESLint
• @graphql-codegen/visitor-plugin-common and @graphql-codegen/typescript-operations from this branch
• NodeJS: 24

Checklist:

• I have followed the CONTRIBUTING doc and the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[changeset-bot]

🦋 Changeset detected

Latest commit: a12ce20

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

This PR includes changesets to release 1 package

Name	Type
@graphql-codegen/visitor-plugin-common	Patch

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