doc: move extensions to _extensions

Move all Sphinx related content to folders prefixed with an underscore.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>
diff --git a/doc/extensions/lexer/DtsLexer.py b/doc/_extensions/lexer/DtsLexer.py
similarity index 100%
rename from doc/extensions/lexer/DtsLexer.py
rename to doc/_extensions/lexer/DtsLexer.py
diff --git a/doc/extensions/lexer/__init__.py b/doc/_extensions/lexer/__init__.py
similarity index 100%
rename from doc/extensions/lexer/__init__.py
rename to doc/_extensions/lexer/__init__.py
diff --git a/doc/extensions/local_util.py b/doc/_extensions/local_util.py
similarity index 100%
rename from doc/extensions/local_util.py
rename to doc/_extensions/local_util.py
diff --git a/doc/extensions/only/eager_only.py b/doc/_extensions/only/eager_only.py
similarity index 100%
rename from doc/extensions/only/eager_only.py
rename to doc/_extensions/only/eager_only.py
diff --git a/doc/extensions/zephyr/__init__.py b/doc/_extensions/zephyr/__init__.py
similarity index 100%
rename from doc/extensions/zephyr/__init__.py
rename to doc/_extensions/zephyr/__init__.py
diff --git a/doc/extensions/zephyr/application.py b/doc/_extensions/zephyr/application.py
similarity index 100%
rename from doc/extensions/zephyr/application.py
rename to doc/_extensions/zephyr/application.py
diff --git a/doc/extensions/zephyr/dtcompatible-role.py b/doc/_extensions/zephyr/dtcompatible-role.py
similarity index 100%
rename from doc/extensions/zephyr/dtcompatible-role.py
rename to doc/_extensions/zephyr/dtcompatible-role.py
diff --git a/doc/extensions/zephyr/html_redirects.py b/doc/_extensions/zephyr/html_redirects.py
similarity index 100%
rename from doc/extensions/zephyr/html_redirects.py
rename to doc/_extensions/zephyr/html_redirects.py
diff --git a/doc/extensions/zephyr/link-roles.py b/doc/_extensions/zephyr/link-roles.py
similarity index 100%
rename from doc/extensions/zephyr/link-roles.py
rename to doc/_extensions/zephyr/link-roles.py
diff --git a/doc/conf.py b/doc/conf.py
index dbb30b6..48a3ad0 100644
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -25,7 +25,7 @@
 
 # Add the 'extensions' directory to sys.path, to enable finding Sphinx
 # extensions within.
-sys.path.insert(0, os.path.join(ZEPHYR_BASE, 'doc', 'extensions'))
+sys.path.insert(0, os.path.join(ZEPHYR_BASE, 'doc', '_extensions'))
 
 # Add the directory which contains the runners package as well,
 # for autodoc directives on runners.xyz.
diff --git a/doc/guides/documentation/index.rst b/doc/guides/documentation/index.rst
index 3fe5817..125dae2 100644
--- a/doc/guides/documentation/index.rst
+++ b/doc/guides/documentation/index.rst
@@ -494,7 +494,7 @@
 zephyr-app-commands Directive
 *****************************
 
-.. include:: ../../extensions/zephyr/application.py
+.. include:: ../../_extensions/zephyr/application.py
    :start-line: 10
    :start-after: '''
    :end-before: '''