Handbook: Add sniff(s) for "Interpolation for Naming Dynamic Hooks" section

Dynamic hooks should be named using interpolation rather than concatenation for readability and discoverability purposes.

Dynamic hooks are hooks that include dynamic values in their tag name, e.g. {$new_status}_{$post->post_type} (publish_post).

Variables used in hook tags should be wrapped in curly braces { and }, with the complete outer tag name wrapped in double quotes. This is to ensure PHP can correctly parse the given variables’ types within the interpolated string.

do_action( "{$new_status}_{$post->post_type}", $post->ID, $post );

Where possible, dynamic values in tag names should also be as succinct and to the point as possible. $user_id is much more self-documenting than, say, $this->id.

Ref: https://make.wordpress.org/core/handbook/best-practices/coding-standards/php/#interpolation-for-naming-dynamic-hooks

Read the linked WordPress PHP coding-standards section first, then locate the repository's PHP_CodeSniffer sniff and test conventions. Done means the ruleset detects dynamic hook names that use concatenation instead of the specified interpolation style, with coverage for the examples described in the issue.