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

scripts/modules/_bl_text_utils/external_editor.py

@@ -0,0 +1,54 @@
+# SPDX-FileCopyrightText: 2023 Blender Authors
+#
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+__all__ = (
+    "open_external_editor",
+)
+
+
+def open_external_editor(filepath, line, column, /):
+    # Internal Python implementation for `TEXT_OT_jump_to_file_at_point`.
+    # Returning a non-empty string represents an error, an empty string for success.
+    import shlex
+    import subprocess
+    from string import Template
+    from bpy import context
+    from bpy.app.translations import pgettext_rpt as rpt_
+
+    text_editor = context.preferences.filepaths.text_editor
+    text_editor_args = context.preferences.filepaths.text_editor_args
+
+    # The caller should check this.
+    assert text_editor
+
+    if not text_editor_args:
+        return rpt_(
+            "Provide text editor argument format in File Paths/Applications Preferences, "
+            "see input field tool-tip for more information",
+        )
+
+    if "$filepath" not in text_editor_args:
+        return rpt_("Text Editor Args Format must contain $filepath")
+
+    args = [text_editor]
+    template_vars = {
+        "filepath": filepath,
+        "line": line + 1,
+        "column": column + 1,
+        "line0": line,
+        "column0": column,
+    }
+
+    try:
+        args.extend([Template(arg).substitute(**template_vars) for arg in shlex.split(text_editor_args)])
+    except Exception as ex:
+        return rpt_("Exception parsing template: {!r}").format(ex)
+
+    try:
+        # With `check=True` if `process.returncode != 0` an exception will be raised.
+        subprocess.run(args, check=True)
+    except Exception as ex:
+        return rpt_("Exception running external editor: {!r}").format(ex)
+
+    return ""