Aliases should be removed for the duration of Arm blocks

[rjmholt]

Except for the ones defined by PSArm.

Alias definitions in PowerShell take precedence over functions, which take precedence over cmdlets.

PSArm defines cmdlet-based keywords with aliases, but resource-specific keywords (i.e. keywords within a Resource block) a defined as functions. This means they will be overridden by other aliases.

For example, a resource with a keyword called type won't be able to use that keyword on Windows because of the type alias for Get-Content.

To fix this, Arm blocks should disable aliases for the duration of their execution and restore them afterward.