Add make.ps1 cmdlet + activateenv command for Windows make scripts (#4087)

* Add missing command to `make.bat`'s help

* Add `activateenv` and `deactivateenv` commands to `make.bat`

* Add help to `Makefile`

* Add `make.ps1` cmdlet

make.bat

@@ -2,31 +2,32 @@
 
 if [%1] == [] goto help
 
-REM This allows us to expand variables at execution
-setlocal ENABLEDELAYEDEXPANSION
-
 goto %1
 
 :reformat
-black "%~dp0."
-exit /B %ERRORLEVEL%
+"%~dp0.venv\Scripts\black" "%~dp0."
+goto:eof
 
 :stylecheck
-black --check "%~dp0."
-exit /B %ERRORLEVEL%
+"%~dp0.venv\Scripts\black" --check "%~dp0."
+goto:eof
 
 :stylediff
-black --check --diff "%~dp0."
-exit /B %ERRORLEVEL%
+"%~dp0.venv\Scripts\black" --check --diff "%~dp0."
+goto:eof
 
 :newenv
 py -3.8 -m venv --clear .venv
-.\.venv\Scripts\python -m pip install -U pip setuptools wheel
+"%~dp0.venv\Scripts\python" -m pip install -U pip setuptools wheel
 goto syncenv
 
 :syncenv
-.\.venv\Scripts\python -m pip install -Ur .\tools\dev-requirements.txt
-exit /B %ERRORLEVEL%
+"%~dp0.venv\Scripts\python" -m pip install -Ur .\tools\dev-requirements.txt
+goto:eof
+
+:activateenv
+CALL "%~dp0.venv\Scripts\activate.bat"
+goto:eof
 
 :help
 echo Usage:
@@ -35,6 +36,9 @@ echo.
 echo Commands:
 echo   reformat                   Reformat all .py files being tracked by git.
 echo   stylecheck                 Check which tracked .py files need reformatting.
+echo   stylediff                  Show the post-reformat diff of the tracked .py files
+echo                              without modifying them.
 echo   newenv                     Create or replace this project's virtual environment.
 echo   syncenv                    Sync this project's virtual environment to Red's latest
 echo                              dependencies.
+echo   activateenv                Activates project's virtual environment.