fix(ui): massive actions failing for plugins with namespaces

[eduardomozart]

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• I have read the CONTRIBUTING document.
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Description

Closes #22614.

When plugins use namespaces for their classes (e.g., GlpiPlugin\Samlsso\RuleSamlCollection), the generated container ID includes backslashes. When this ID is used in an inline JavaScript snippet to generate a jQuery selector, the single backslash evaluates properly as a JavaScript string literal, but fails when evaluated by jQuery's CSS selector engine. CSS requires literal backslashes to be double-escaped \\.

This PR ensures that container IDs used in inline jQuery selectors within Html.php explicitly have their backslashes escaped for CSS (by passing the string through addcslashes($container_id, '\\') prior to jsescape()). This correctly emits four backslashes \\\\ into the JavaScript string literal, which evaluates to a double backslash \\ in JavaScript, allowing jQuery to properly target the element ID.

• Fixed Html::getCheckAllAsCheckbox()
• Fixed Html::getCheckboxesFilter()
• Fixed Html::showMassiveActionsBlock()
• Added test coverage in HtmlTest::testMassiveActionContainerIdEscaping

Screenshots (if appropriate):