Multiline fields in forms have no visible label

[navarr]

Preconditions

1. Magento CE 2.1.2
2. Custom <uiComponent /> form

Steps to reproduce

1. Create a <field>
2. Set it's formElement to multiline
3. Load the form in the browser

(Example <field>):

    <field name="street">
        <argument name="data" xsi:type="array">
            <item name="config" xsi:type="array">
                <item name="label" xsi:type="string" translate="true">Street</item>
                <item name="dataType" xsi:type="string">text</item>
                <item name="size" xsi:type="number">2</item>
                <item name="formElement" xsi:type="string">multiline</item>
                <item name="visible" xsi:type="boolean">true</item>
                <item name="source" xsi:type="string">general</item>
                <item name="validation" xsi:type="array">
                    <item name="required-entry" xsi:type="boolean">true</item>
                </item>
            </item>
        </argument>
    </field>

Expected result

(The label "Street" to be visible to the left of the top input)

Actual result

The label ("Street" in this case) matches the following CSS rule:

.admin__field legend.admin__field-label {
    opacity: 0;
}

Rendering it invisible.

The less responsible for this was added to the code in this commit

[tkacheva]

Internal ticket MAGETWO-61202