feat(coverage): add sourceFinder property to coverage options

[teoeter]

Description

This PR introduces a new feature that addresses #8324 by exposing a function through the coverage configuration, allowing users to modify the file path and content used by istanbul-lib-coverage.

The function returns file path and can be customized to alter the content or path as needed. By default, it performs filesystem lookups based on the provided path.

This change also resolves an issue with Angular 20 projects using Vitest, where source paths are not correctly resolved trough istanbul-lib-coverage.

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