Account for Svelte class bindings at the start of a line

[bradlc]

Fixes #4181

This PR updates the Svelte class binding regular expression so that it catches instances at the start of a line.

Consider the following example:

<button
  class:bg-red-500={current === 'foo'}
>
  Click me
</button>

Because the class extractor runs for each trimmed line separately, in this case it runs against class:bg-red-500={current === 'foo'}. The regular expression did not match the class binding because there is no whitespace before it.

The regular expression has been updated to look for either whitespace or the start of the string, which fixes the issue.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.84%. Comparing base (9b1e843) to head (ce1a0ee).
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Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4187   +/-   ##
=======================================
  Coverage   86.84%   86.84%           
=======================================
  Files         341      341           
  Lines        4836     4836           
  Branches      919      919           
=======================================
  Hits         4200     4200           
  Misses        561      561           
  Partials       75       75           

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[adamwathan]

Thanks @bradlc!