This patch adds support to multiple diffs. These are possible
due to soft assertions.
Drive-by: rename second screenshot in `toHaveScreenshot` failure when
re-generating expectations from "expected" to "previous".
Soft expects will still fail the test, but will not abort it's execution. As a consequence of this:
- `TestResult` now might have multiple errors, which is reflected with a new `testResult.erros: TestError[]` field.
- `TestInfo` now might have multiple errors as well, which is reflected with a new `testInfo.errors: TestError[]` field.
Fixes#7819
