Refactor SVG loading and dimension handling

[roborourke]

Description of the Change

Corrects the filters in the svg_dimensions method to return the documented value and data type, and additionally sends the attachment ID as the last parameter because it's more useful to do things with than the file path.

Closes #277

How to test the Change

The following snippet no longer throws a fatal error.

add_filter( 'safe_svg_use_width_height_attributes', function ( bool $use_width_height, string $svg ) {
	return $use_width_height;
}, 10, 2 );

Changelog Entry

Changed - Added $attachment_id argument to filters safe_svg_use_width_height_attributes and safe_svg_dimensions.
Fixed - Inconsistent or incorrect data type for $svg argument in the filters safe_svg_use_width_height_attributes and safe_svg_dimensions.

Credits

Props @roborourke

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.