Improve logging and log visibility

[MichelleBlanchette]

Refer to WordPress's usage in the source code of this function: https://developer.wordpress.org/reference/functions/_deprecated_function/

The trigger_error() function has all the verbosity I've been wanting, such as the file and line number where called.

Applicable constants are here: https://www.php.net/manual/en/errorfunc.constants.php

• E_USER_ERROR
• E_USER_WARNING
• E_USER_NOTICE
• E_USER_DEPRECATED

Should also probably wrap error logging within checks for if ( WP_DEBUG ) like WordPress core does, as well. 🤷
^ No, because I don't want to require this to help debug something for someone.

[MichelleBlanchette]

Better yet, all logging should be handled custom and visible in an admin screen for the plugin! Logging to the server doesn't help with support requests where I simply gain access to their WordPress admin. (And I definitely don't want SSH access to their server, anyways!)

[MichelleBlanchette]

A few thoughts I just randomly had on this:

• Log file should be in wp-content/uploads folder so it doesn't get deleted every time the plugin files are updated (also, see about WordPress VIP's filesystem restrictions which permit that folder only)
• Download button should be made available in wp-admin to download the log file so it can be provided to technical support (we should never have a reason to log into a user's system)
• Log function can probably mimic trigger_error()'s verbosity by getting the prior stacktrace function automatically (we shouldn't need to manually pass __FUNCTION__ every time like wp_trigger_error() expects... 🙄
• Setting to enable or disable logging, default to disabled since users should only need logging to debug issues (like us in active development)