[plugin model] use internal visibility for content modules which are used from test plugins (IJPL-206556)

Currently, we don't have a special 'visible for testing' variant of the visibility modifier, so we need to mark such modules as internal to avoid errors after the visibility checks are enabled at runtime.

Reviewed in IJ-MR-180677.

GitOrigin-RevId: 1dcff728cc567e0c9c4055285b279402b7e5e030

python/services/internal-impl/resources/intellij.python.community.services.internal.impl.xml

@@ -1,4 +1,4 @@
-<idea-plugin>
+<idea-plugin visibility="internal">
   <dependencies>
     <module name="intellij.python.community"/>
     <module name="intellij.python.psi.impl"/>

python/services/shared/resources/intellij.python.community.services.shared.xml

@@ -1,4 +1,4 @@
-<idea-plugin>
+<idea-plugin visibility="internal">
   <dependencies>
     <module name="intellij.python.community.execService.python"/>
     <module name="intellij.python.community"/>

python/services/system-python/resources/intellij.python.community.services.systemPython.xml

@@ -1,4 +1,4 @@
-<idea-plugin>
+<idea-plugin visibility="internal">
   <dependencies>
     <module name="intellij.python.community"/>
     <module name="intellij.python.psi.impl"/>