Clear and concise description of the problem

Continuation for:

• feat(coverage): v8 experimental AST-aware remapping #7736

There should be no need for old non-AST based remapping (v8-to-istanbul) once vitest@3.2.0 has been released. However the coverage diffs between these two remapping methods is quite much, so we should consider this as breaking change. Users are very likely seeing different, more accurate results with the new experimentalAstAwareRemapping option.

Removing the old remapping method simplifies @vitest/coverage-v8 codebase a lot.

Suggested solution

• Remove v8-to-istanbul completely
• Remove experimentalAstAwareRemapping option and default to AST based remapping via ast-v8-to-istanbul always

Alternative

No response

Additional context

No response

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.