ComplexQZ would try to apply a Jacobi rotation to an empty block, which triggers a warning in static analyzers, since the corresponding `Eigen::Map` object will contain a `nullptr`.
See merge request libeigen/eigen!2043
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### Description
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More ComplexQZ fixes.
Extra semicolons are triggering some warnings and errors with `-Werror`.
Moved the `Sparse` import up to the umbrella header to avoid IWYU exports.
### Reference issue
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See merge request libeigen/eigen!2036
The `Options` of the new `hCoeffs` vector do not necessarily match
those of the `MatrixType`, leading to build errors. Having the
`CoeffVectorType` be a template parameter relieves this restriction.
Should have been 0.5 to widen the bounds, since this is inverse
precision. Setting to 0.5, however, leads to many more failing
tests at Google, so reverting to 1 for now.
Adjust the relaxation step to use the condition
```
abs(subdiag[i]) <= epsilon * sqrt(abs(diag[i]) + abs(diag[i+1]))
```
for setting the subdiagonal entry to zero.
Also adjust Wilkinson shift for small `e = subdiag[end-1]` -
I couldn't find a reference for the original, and it was not
consistent with the Wilkinson definition.
Fixes#2191.
