Based on @PowerShell/powershell-committee decision at PowerShell/PowerShell-RFC#133 (comment), we should:

• PSCore6 currently will create $env:PSModulePath from config.json file, a new setting EnvVarToAppendToPSModulePath with value PSModulePath (this means the $PSHOME/Modules and user paths are first, then appends the $env:PSModulePath from the system)
• Some logic needs to be retained so child PSCore6 trims any duplicates in $env:PSModulePath
• When pwsh is started, we preserve the original $env:PSModulePath. Have whitelist to special case powershell.exe and powershell_ise.exe so when they are started within pwsh, they receive the original $env:PSModulePath. In all other cases, they inherit the current $env:PSModulePath.
• Since modules are auto-discovered by newest version and not by order of the path, there is a scenario where starting different versions of pwsh from pwsh may result in unexpected behavior.