PyAPI: make internal modules explicitly "private"

Rename modules in `./scripts/modules/` to use an underscore prefix to
make it clear they aren't intended to be part of public API's. This
also means there is no implication that these modules should be stable,
allowing us to change them based on Blender's internal usage.

The following modules have been marked as private:

- `animsys_refactor`
- `bl_console_utils`
- `bl_i18n_utils`
- `bl_previews_utils`
- `bl_rna_utils`
- `bl_text_utils`
- `bl_ui_utils`
- `bpy_restrict_state`
- `console_python`
- `console_shell`
- `graphviz_export`
- `keyingsets_utils`
- `rna_info`
- `rna_manual_reference`
- `rna_xml`

Note that we could further re-arrange these modules
(under `_bpy_internal` in some cases), this change is mainly to mark
them as private, further changes can be handed on a case-by-case basis.

Ref !147773

tests/python/bl_load_py_modules.py

@@ -18,8 +18,8 @@ import os
 # The trailing components of the path are used instead of the module name.
 # Both script files & directories are supported which prevents searching inside the directory.
 EXCLUDE_MODULE_PATHS = {
-    "bl_i18n_utils",
-    "bl_previews_utils",
+    "_bl_i18n_utils",
+    "_bl_previews_utils",
     "cycles",
 
     # These tests which run stand-alone and aren't imported as modules.

tests/python/bl_rna_manual_reference.py

@@ -17,7 +17,7 @@ VERBOSE = False
 
 
 def test_data():
-    import rna_manual_reference
+    import _rna_manual_reference as rna_manual_reference
 
     assert isinstance(rna_manual_reference.url_manual_mapping, tuple)
     for i, value in enumerate(rna_manual_reference.url_manual_mapping):
@@ -37,7 +37,7 @@ def lookup_rna_url(rna_id, visit_indices):
     A local version of ``WM_OT_doc_view_manual._lookup_rna_url``
     that tracks which matches are found.
     """
-    import rna_manual_reference
+    import _rna_manual_reference as rna_manual_reference
     from fnmatch import fnmatchcase
     rna_id = rna_id.lower()
     for i, (pattern, url_suffix) in enumerate(rna_manual_reference.url_manual_mapping):
@@ -51,7 +51,7 @@ def lookup_rna_url(rna_id, visit_indices):
 def test_lookup_coverage():
 
     def rna_ids():
-        import rna_info
+        import _rna_info as rna_info
         struct = rna_info.BuildRNAInfo()[0]
         for struct_id, v in sorted(struct.items()):
             props = [(prop.identifier, prop) for prop in v.properties]
@@ -96,7 +96,7 @@ def test_lookup_coverage():
     print("---------------------------------------")
     print("Unused RNA Patterns Known to the Manual")
 
-    import rna_manual_reference
+    import _rna_manual_reference as rna_manual_reference
     for i, (pattern, url_suffix) in enumerate(rna_manual_reference.url_manual_mapping):
         if i not in visit_indices:
             print(pattern, url_suffix)
@@ -118,7 +118,7 @@ def test_language_coverage():
 def test_urls():
     import os
     import sys
-    import rna_manual_reference
+    import _rna_manual_reference as rna_manual_reference
 
     import urllib.error
     from urllib.request import urlopen

tests/python/rna_info_dump.py

@@ -97,7 +97,7 @@ def api_dump(use_properties=True, use_functions=True):
         data.insert(0, "# * properties *")
         return data
 
-    import rna_info
+    import _rna_info as rna_info
     struct = rna_info.BuildRNAInfo()[0]
     data = []