Refactor VarRenderer class to use candidates for class loading

[TDannhauer]

Fix Horde_Core_Ui_VarRenderer::factory() app renderer resolution

Summary

• Fix Horde_Core_Ui_VarRenderer::factory() so lowercase application IDs in varrenderer_driver (e.g. ['kronolith', 'html']) resolve to the correct {App}_Ui_VarRenderer_{Driver} class via Composer autoload.
• Remove the broken legacy include_once fallback that could instantiate Horde_Core_Ui_VarRenderer_* after loading an application renderer file.
• Use Horde\Util\HordeString for string normalization instead of deprecated Horde_String.

Problem

Horde applications extend Horde_Core_Ui_VarRenderer_Html with app-specific classes (e.g. Kronolith_Ui_VarRenderer_Html, Turba_Ui_VarRenderer_Html) to render custom form field types. Forms pass a driver tuple to the form renderer:

['varrenderer_driver' => ['kronolith', 'html']]

When the factory cannot load the application renderer, form fields fall back to Horde_Core_Ui_VarRenderer_Html::_renderVarInputDefault(), which outputs inline HTML such as:

Warning: Unknown variable type …

Those messages are usually not written to the application log.

Root cause

In Horde_Core_Ui_VarRenderer::factory():

1. The driver segment was normalized with Horde_String::ucfirst() (html → Html).
2. The application segment was used verbatim (kronolith → kronolith).
3. The factory requested class kronolith_Ui_VarRenderer_Html, which is not in Composer’s classmap (Kronolith_Ui_VarRenderer_Html is).

Autoload failed. The legacy path then:

1. include_once’d the app’s lib/Ui/VarRenderer/Html.php (defining Kronolith_Ui_VarRenderer_Html, etc.).
2. Checked class_exists('Horde_Core_Ui_VarRenderer_Html') — always true.
3. Returned new Horde_Core_Ui_VarRenderer_Html() — the base renderer without app-specific _renderVarInput_* methods.

This regressed as applications renamed renderers to {App}_Ui_VarRenderer_{Driver} for classmap autoloading without updating the factory fallback.

Solution

lib/Horde/Core/Ui/VarRenderer.php

• Resolve the renderer class through autoload only (no manual include_once or registry fileroot paths).
• Try candidate class names in order:
  1. {Ucfirst(app)}_Ui_VarRenderer_{Ucfirst(driver)} — matches Composer classmap names.
  2. {app}_Ui_VarRenderer_{Ucfirst(driver)} — only if different from (1), for callers that already pass a capitalized app id.
  3. Horde_Core_Ui_VarRenderer_{Ucfirst(driver)} — fallback when an app has no custom renderer.
• Use Horde\Util\HordeString::ucfirst() and basename() for driver normalization.

Package

horde/core — Horde_Core_Ui_VarRenderer::factory() only.

Test plan

• In an application with a custom lib/Ui/VarRenderer/Html.php and lowercase varrenderer_driver (e.g. Kronolith calendar edit, Turba contact edit, Ingo filter forms), open a form that uses app-specific field types and confirm controls render correctly (no “Unknown variable type” warnings).
• Trigger a reload action on a field that uses Horde_Form_Action_reload and confirm the re-rendered form still uses the application renderer.
• Confirm a form with varrenderer_driver set to 'html' only (no app segment) still uses Horde_Core_Ui_VarRenderer_Html.
• Confirm an application without a custom VarRenderer still receives Horde_Core_Ui_VarRenderer_Html when passing ['someapp', 'html'].

Notes for reviewers

• Failures were user-visible HTML warnings from the default var renderer, not thrown exceptions.
• Call sites may continue passing lowercase registry app ids; no caller changes are required in this PR.