[fragment-matcher] fix: indentation of generated code

[cpruijsen]

Description

Fix indentation in packages/plugins/other/fragment-matcher/src/index.ts so TypeScript and JavaScript declarations start at column zero.
Interface members use two-space indentation to match the serialized JSON.
The fix also applies to an empty possibleTypes map.

Related #6600

Type of change

• Bug fix

Screenshots/Sandbox (if appropriate/relevant):

The TypeScript output for a schema without interfaces or unions now includes:

export interface PossibleTypesResultData {
  possibleTypes: {
    [key: string]: string[]
  }
}
const result: PossibleTypesResultData = {
  "possibleTypes": {}
};
export default result;

How has this been tested?

Two new tests in packages/plugins/other/fragment-matcher/tests/plugin.spec.ts compare the JavaScript and TypeScript output as exact strings. Both fail without this change and pass with it, and the other 14 package tests still pass.

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

Further comments

The fix removes wrapper padding and keeps two-space JSON indentation.
The alternative was six extra spaces on each serialized JSON line.

[changeset-bot]

🦋 Changeset detected

Latest commit: ea3dea2

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/fragment-matcher	Patch

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