[PowershellV2] Fix powershell execution script to fail on wrong targettype

[ghost]

Task name: PowershellV2

Description:

• Add additional condition to validate if target path is 'filepath' or 'inline', otherwise write error
• Add localization string for error message

Documentation changes required: (Y/N) N

Added unit tests: (Y/N) N

Attached related issue: (Y/N) https://github.com/microsoft/build-task-team/issues/1355

Checklist:

• Task version was bumped - please check instruction how to do it
• Checked that applied changes work as expected

[anatolybolshakov]

LGTM, thanks!
Btw does it mean that there could be the same issue for other task inputs with type: radio and Powershell execution handlers? If so - could it make sense to recheck all Powershell handler tasks also?
cc @alexander-smolyakov