FileUtils.TestServerNamesDefaultFileName_get uses '… + @"\\" + …'
construct to build the default path for the test server names file.
While escaping a backslash in a verbatim string is a typo, the
approach was error-prone. Replace string manipulation and environment
variables magic with calls to well-tested library functions.
GetSettingFileContent() displays a message on switching to VS Code
settings when SQL connection instances were configured.
Move the message to the branch for the absent test configuration file.
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