fix(locale-modal): replaced placeholder color for a bolder one (carbo…

…n-design-system#4896)

### Related Ticket(s)
carbon-design-system#4802

### Description

The previous placeholder color for the Web Components version was failing contrast ratio testing. Changed the placeholder text to match the `$text-02` token used in the React version, where the contrast ratio has been fixed.

### Changelog

**Changed**

- `<dds-search>` placeholder color changed to `$text-02` to match React version

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<!-- *** "package: services": Services -->
<!-- *** "package: utilities": Utilities -->
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packages/web-components/src/components/search/search.scss

@@ -1,5 +1,5 @@
 //
-// Copyright IBM Corp. 2020
+// Copyright IBM Corp. 2020, 2021
 //
 // This source code is licensed under the Apache-2.0 license found in the
 // LICENSE file in the root directory of this source tree.
@@ -31,4 +31,15 @@
   &[color-scheme='light'] {
     @extend .#{$prefix}--search--light;
   }
+
+  /**
+   * We are deliberatey diverging from the global helper mixins for placeholder, found here:
+   * (https://github.com/carbon-design-system/carbon/blob/v10.25.0/packages/components/src/globals/scss/_helper-mixins.scss#L44-L51)
+   * 
+   * The reason for this being that the current placeholder color fails contrast testing, 
+   * while this replacement color passes testing.
+   */
+  ::placeholder {
+    color: $text-02;
+  }
 }