Update editable installation instruction to use editable_mode=strict

Avoid "module not found" errors on VSCode
https://microsoft.github.io/pyright/#/import-resolution?id=editable-installs

Makefile

@@ -14,7 +14,7 @@ clean-pyc:
 	find . -name '*~' -exec rm -f {} +
 
 develop: clean-pyc
-	pip install -e .[testing,docs]
+	pip install -e .[testing,docs] --config-settings editable-mode=strict
 	npm install --no-save && npm run build
 
 lint-server:

docs/README.md

@@ -2,7 +2,7 @@
 
 These are Sphinx docs, automatically built at [https://docs.wagtail.org](https://docs.wagtail.org) when the `main` branch is committed to GitHub. To build them locally, install Wagtail's development requirements (in the root Wagtail directory):
 
-    pip install -e .[testing,docs]
+    pip install -e .[testing,docs] --config-settings editable-mode=strict
 
 To build the documentation for browsing, from this directory run:
 

docs/contributing/developing.md

@@ -29,7 +29,7 @@ cd wagtail
 **With your preferred [virtualenv activated](virtual_environment_creation),** install the Wagtail package in development mode with the included testing and documentation dependencies:
 
 ```sh
-pip install -e ."[testing,docs]" -U
+pip install -e ."[testing,docs]" --config-settings editable-mode=strict -U
 ```
 
 Install the tool chain for building static assets:
@@ -47,7 +47,7 @@ npm run build
 Any Wagtail sites you start up in this virtualenv will now run against this development instance of Wagtail. We recommend using the [Wagtail Bakery demo site](https://github.com/wagtail/bakerydemo/) as a basis for developing Wagtail. Keep in mind that the setup steps for a Wagtail site may include installing a release version of Wagtail, which will override the development version you've just set up. In this case, to install the local Wagtail development instance in your virtualenv for your Wagtail site:
 
 ```sh
-pip install -e path/to/wagtail"[testing, docs]" -U
+pip install -e path/to/wagtail"[testing, docs]" --config-settings editable-mode=strict -U
 ```
 
 Here, `path/to/wagtail` is the path to your local Wagtail copy.
@@ -291,7 +291,7 @@ The Wagtail documentation is built by Sphinx. To install Sphinx and compile the
 # Starting from the wagtail root directory:
 
 # Install the documentation dependencies
-pip install -e .[docs]
+pip install -e .[docs] --config-settings editable-mode=strict
 # or if using zsh as your shell:
 #    pip install -e '.[docs]' -U
 # Compile the docs

tox.ini

@@ -5,7 +5,7 @@ usedevelop = True
 envlist = py{39,310,311,312,313}-dj{42,51,52stable,main}-{sqlite,postgres,mysql,mssql}-{elasticsearch8,elasticsearch7,noelasticsearch}-{customuser,emailuser}-{tz,notz},
 
 [testenv]
-install_command = pip install -e ".[testing]" -U {opts} {packages}
+install_command = pip install -e ".[testing]" --config-settings editable-mode=strict -U {opts} {packages}
 commands =
     elasticsearch7: coverage run runtests.py wagtail.search wagtail.documents wagtail.images --elasticsearch7
     elasticsearch8: coverage run runtests.py wagtail.search wagtail.documents wagtail.images --elasticsearch8