AttrCursor: Remove forceErrors

[edolstra]

Motivation

This should remove all "cached failure of attribute X" messages by forcing evaluation of the original value when it's needed to show the exception to the user.

Context

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[Mic92]

Actually I am not longer able to reproduce the eval error with nix 2.22.0, also it happens for nix 2.18. Also the test you wrote works even if the fix is not applied.

[edolstra]

@Mic92 I can't reproduce that. The test does fail for me without the fix:

    +(eval-cache.sh:21) expect 1 nix build /tmp/nix-shell.vnDGIZ/nix-test/flakes/eval-cache/eval-cache-flake#foo.bar
    +(eval-cache.sh:21) grepQuiet 'error: breaks'
    +(/home/eelco/Dev/nix-master/tests/functional/common/vars-and-functions.sh:279) grep 'error: breaks'
    +(eval-cache.sh:22) grepQuiet 'error: breaks'
    +(/home/eelco/Dev/nix-master/tests/functional/common/vars-and-functions.sh:279) grep 'error: breaks'
    +(eval-cache.sh:22) expect 1 nix build /tmp/nix-shell.vnDGIZ/nix-test/flakes/eval-cache/eval-cache-flake#foo.bar
    ++(eval-cache.sh:22) onError
    ++(/home/eelco/Dev/nix-master/tests/functional/common/vars-and-functions.sh:250) set +x
    eval-cache.sh: test failed at:
      main in eval-cache.sh:22