DX: use numeric_literal_separator

[keradus]

ref #6761

[coveralls]

Pull Request Test Coverage Report for Build 4038978590

• 61 of 64 (95.31%) changed or added relevant lines in 41 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 92.944%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/AbstractPhpdocToTypeDeclarationFixer.php	0	1	0.0%
src/Fixer/NamespaceNotation/CleanNamespaceFixer.php	1	2	50.0%
src/Tokenizer/Tokens.php	1	2	50.0%

Totals
Change from base Build 4037042600:	0.0%
Covered Lines:	22618
Relevant Lines:	24335

---

💛 - Coveralls

[kubawerlos]

@keradus any plans to follow up with some auto review check no new code will be inconsistent.

Something like 👇🏼 in ProjectCodeTest.php, maybe?

    /**
     * @dataProvider provideSrcClassCases
     * @dataProvider provideTestClassCases
     */
    public function testUsingLiteralSeparator(string $className): void
    {
        $tokens = Tokens::fromCode(file_get_contents((new \ReflectionClass($className))->getFileName()));

        foreach ($tokens->findGivenKind(T_LNUMBER) as $token) {
            if ((int) str_replace('_', '', $token->getContent()) < 5_00_00 || 5 !== preg_match_all('/\d/', $token->getContent())) {
                static::assertMatchesRegularExpression('/^[^_]+$/', $token->getContent());

                continue;
            }

            static::assertMatchesRegularExpression(
                '/^\d{1}_\d{2}_\d{2}$/',
                $token->getContent(),
                sprintf('PHP_VERSION_ID incorrectly formatted in %s (must be like %s)', $className, 8_20_00)
            );
        }
    }

[keradus]

I would be very open for it, but wont be able to put effort for it myself.