Follows the approach used in Initialise-Idf.ps1 created by the tools
installer. This is the closes equivalent of "alias" used in export.bat
Closes https://github.com/espressif/esp-idf/issues/9849
With strict debugging, i.e. `Set-PSDebug -strict`, execution of export.ps1 will
report the following error:
```
The variable '$envars_array' cannot be retrieved because it has not been set.
At C:\path\to\export.ps1:15 char:1
+ $envars_array # will be filled like:
+ ~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (envars_array:String) [], RuntimeException
+ FullyQualifiedErrorId : VariableIsUndefined
```
Closes https://github.com/espressif/esp-idf/pull/7819