Remove <pre> tags from _deprecated_constructor()

[SergeyBiryukov]

The _deprecated_constructor() function introduced in [32989] wraps the replacement name in <pre> tags, which breaks the message into multiple lines and looks weird. It's also inconsistent with other _deprecated_*() functions, which don't wrap the replacement name in any tags:

• _deprecated_function()
• _deprecated_file()
• _deprecated_argument()
• _deprecated_hook()

If anything, <code> should be used here instead of <pre> to keep the message on a single line.

Example of a current message:

Deprecated: The called constructor method for WP_Widget in WP_Widget is deprecated since version 4.3.0! Use

__construct()

instead. in wp-includes/functions.php on line 4711

The expected result:

Deprecated: The called constructor method for WP_Widget in WP_Widget is deprecated since version 4.3.0! Use __construct() instead. in wp-includes/functions.php on line 4711

[SergeyBiryukov]

In 46633:

General: Wrap the error message in _deprecated_constructor() in <code> tags instead of <pre>.

Props aftabmuni.
Fixes #48483.