Fix load order of view.xml when loading Swatch config

[pmclain]

Description

Fix load/merge order of view.xml conifg in \Magento\Swatches\Helper\Media to match \Magento\Catalog\Helper\Image.

Fixed Issues (if relevant)

1. Image Swatch size change not working #12647

Manual testing scenarios

1. Create new theme named to preceed 'Magento' alphabetically. ie 'Acme\default'
2. Add view.xml to theme's etc directory altering the swatch images sizes. Sample

<?xml version="1.0"?>
<view xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:Config/etc/view.xsd">
    <media>
        <images module="Magento_Catalog">
            <image id="swatch_image" type="swatch_image">
                <width>48</width>
                <height>48</height>
            </image>
            <image id="swatch_thumb" type="swatch_thumb">
                <width>130</width>
                <height>130</height>
            </image>
            <image id="swatch_image_base" type="swatch_image">
                <width>48</width>
                <height>48</height>
            </image>
            <image id="swatch_thumb_base" type="swatch_thumb">
                <width>130</width>
                <height>130</height>
            </image>
        </images>
    </media>
</view>

3. Enable theme in admin panel.
4. Flush cache: bin/magento cache:flush
5. Deploy static content: bin/magento setup:static-content:deploy
6. Navigate to product list page containing visual swatch filters and validate swatch image dimensions match those specified in view.xml

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[dmanners]

Hi @pmclain thank you for this pull request. I will start to process it and let you know if I need anything else from you.

[dmanners]

HI @pmclain I do have a question. How does this code change effect when you have a dependent theme? For example if you have a theme loaded that it's self does not have a swatch_image settings but has a parent theme that does have this setting does it still get loaded?

[pmclain]

@dmanners Yes. When the active theme's view.xml does not contain a node the parent is used.

[josefbehr]

@pmclain Thanks for this contribution! Would you be able and willing to provide a backport of this PR to the 2.2 branch?