BUG: Wrong separator used in get_synonyms on Windows

[nymwo]

Describe the bug

The Synonym feature doesn't work when hosted on Windows.

In wp-content\plugins\elasticpress\includes\classes\Feature\Search\Synonyms.php we can se that the synonyms are separated (explode) by PHP_EOL, which is \r\n on Windows:

	public function get_synonyms() {
		$synonyms_raw = $this->get_synonyms_raw();
		$synonyms     = array_values(
			array_filter(
				array_map( [ $this, 'validate_synonym' ], explode( PHP_EOL, $synonyms_raw ) )
			)
		);

		/**
		 * Filter array of synonyms to add to a custom synonym filter.
		 *
		 * @hook ep_synonyms
		 * @return  {array} The new array of search synonyms.
		 */
		return apply_filters( 'ep_synonyms', $synonyms );
	}

But it looks like $this->get_synonyms_raw() always returns a string with synonyms separated by \n. On Linux, PHP_EOL is defined as \n, so this issue does not appear when running on that OS.

Changing PHP_EOL to "\n" resolves the issue on Windows.

Steps to Reproduce

1. Host on a Windows environment
2. Add synonyms
3. Try to use those synonyms

Screenshots, screen recording, code snippet

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Environment information

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WordPress and ElasticPress information

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