Merge topic 'update-to-c++17'

39431b7e Add change log for c++17 requirement
859cd6a8 README.md: update minimum compiler dependencies
245ea7ef Resolve an ambiguous call issue setting nlohmann::json value from vtkStdString
488ae974 vtkCompilerWarningFlags: ignore noisy attribute warnings from GCC < 9.1
0500438a ci el7-mindeps: use image with devtoolset-8
84bc1abf ci: add devtoolset-8 to launcher for el7-mindeps builder
3dc003b3 ci: update el7-mindeps to install devtoolset-8
bca44ed6 vtkTableBasedClipCases.cxx: remove unneeded implementation file
...

Acked-by: Kitware Robot <kwrobot@kitware.com>
Acked-by: buildbot <buildbot@kitware.com>
Merge-request: !11049