[REF][PHP8.2] Avoid dynamic properties in CRM_Case_Form_CaseView

[braders]

Overview

Avoid dynamic properties in CRM_Case_Form_CaseView.

Before

Several properties set and retreived dynamically, which is deprecated in PHP 8.2. See https://lab.civicrm.org/dev/core/-/issues/3833 for context.

After

The properties are defined upfront, and are not dynamic.

I've also ensured _showRelatedCases is always a boolean (rather than simply a "truthy" value), which better reflects how it is used.

Also removes an unused $cId variable.

Technical Details

Most of these should probably be private, but given the number of dynamic properties across the codebase if we take that approach everywhere we're bound to break some extensions. For now I've marked the properties as internal to hopefully discourage usage by extensions, and the visibility can be revisited in future.

[civibot]

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