Refactor UPE Appearance transients constants

[brettshumaker]

Description

WooPayments now has several transients related to UPE themes and styles. While working on #8249, I created a general APPEARANCE_THEME_TRANSIENTS constant on the WC_Payment_Gateway_WCPay class to be able to access these transients’ names (from outside the class) without having to remember each individual constant (or transient) name. It resulted in being able to access the theme for a specific location and context in a readable way like this:

$themes   = \WC_Payment_Gateway_WCPay::APPEARANCE_THEME_TRANSIENTS;
$location = 'checkout'; // The locations where we currently track the theme are 'checkout', 'product_page', and 'cart'.
$context  = 'blocks'; // The contexts we're currently tracking the theme are 'blocks', and 'classic'.
$theme    = $themes[ $location ][ $context ]; 

I think we should refactor our usage of the appearance and theme transients to follow a similar format and update how we’re accessing these transient names throughout the plugin.

Acceptance criteria

• All transient names related to UPE appearance are contained within one constant.
• All existing uses of these transient constants are refactored to use the new constant.
• All UPE "locations" are utilizing the correct transient for the given location and context.

Dev notes

Here’s the first idea I had on structure:

const UPE_APPEARANCE_TRANSIENTS = [
     'checkout' => [
        'blocks' => [
            'appearance' => self::WC_BLOCKS_UPE_APPEARANCE_TRANSIENT,
            'theme'      => self::WC_BLOCKS_UPE_APPEARANCE_THEME_TRANSIENT,
        ],
        'classic' => [
            'appearance' => self::UPE_APPEARANCE_TRANSIENT,
            'theme'      => self::UPE_APPEARANCE_THEME_TRANSIENT,
        ],
    ],
    'product_page' => [
        'blocks' => [
            'appearance' => self::UPE_BNPL_PRODUCT_PAGE_APPEARANCE_TRANSIENT,
            'theme'      => self::UPE_BNPL_PRODUCT_PAGE_APPEARANCE_THEME_TRANSIENT,
        ],
        'classic' => [
            'appearance' => self::UPE_BNPL_PRODUCT_PAGE_APPEARANCE_TRANSIENT,
            'theme'      => self::UPE_BNPL_PRODUCT_PAGE_APPEARANCE_THEME_TRANSIENT,
        ],
    ],
    'cart' => [
        'blocks' => [
            'appearance' => self::UPE_BNPL_CART_BLOCK_APPEARANCE_TRANSIENT,
            'theme'      => self::UPE_BNPL_CART_BLOCK_APPEARANCE_THEME_TRANSIENT,
        ],
        'classic' => [
            'appearance' => self::UPE_BNPL_CLASSIC_CART_APPEARANCE_TRANSIENT,
            'theme'      => self::UPE_BNPL_CLASSIC_CART_APPEARANCE_THEME_TRANSIENT,
        ],
    ],
];

That would give an access structure like $transients[ $location ][ $context ][ $type ] though I’m open to other ideas as well.