Deduplicate PHP version branching in RectorConfigBuilder

[TomasVotruba]

Follow-up to #8225, same class. Two methods mapped a pile of bool arguments to a PHP version through long branch chains, and nine more methods repeated the same three statements.

withPhpSets()

Sixteen bool arguments were resolved by nine early-return blocks followed by a seven-branch elseif chain:

if ($php53) {
    $this->withPhp53Sets();
    return $this;
}

if ($php54) {
    $this->withPhp54Sets();
    return $this;
}

// ... seven more of these ...

if ($php80) {
    $targetPhpVersion = PhpVersion::PHP_80;
} elseif ($php81) {
    $targetPhpVersion = PhpVersion::PHP_81;
} elseif ($php82) {
// ... five more ...
} else {
    throw new InvalidConfigurationException('Invalid PHP version set');
}

Now one map:

$pickedPhpVersions = array_keys(array_filter([
    PhpVersion::PHP_53 => $php53,
    PhpVersion::PHP_54 => $php54,
    // ...
    PhpVersion::PHP_86 => $php86,
]));

This also replaces the func_get_args() call that the arity checks were built on, so the "pick only one version" and "resolve from composer.json" branches read off the same array. The unreachable 'Invalid PHP version set' branch goes away — a non-empty picked list always has exactly one entry by that point.

The argument order in the signature is unchanged, including $php84/$php85/$php86 staying last for positional-call BC.

withDowngradeSets()

Same shape, nine branches:

-if ($php84) {
-    $this->sets[] = DowngradeLevelSetList::DOWN_TO_PHP_84;
-} elseif ($php83) {
-    $this->sets[] = DowngradeLevelSetList::DOWN_TO_PHP_83;
-} elseif ($php82) {
-// ... six more ...
-}
+$pickedDowngradeSets = array_keys(array_filter([
+    DowngradeLevelSetList::DOWN_TO_PHP_84 => $php84,
+    DowngradeLevelSetList::DOWN_TO_PHP_83 => $php83,
+    // ...
+]));

The nine withPhpNNSets() methods

Each was the same three statements with one constant swapped:

public function withPhp70Sets(): self
{
    $this->isWithPhpSetsUsed = true;

    $this->sets = array_merge($this->sets, PhpLevelSetResolver::resolveFromPhpVersion(PhpVersion::PHP_70));

    return $this;
}

becomes

public function withPhp70Sets(): self
{
    return $this->addPhpLevelSets(PhpVersion::PHP_70);
}

withPhpSets() uses the same private helper for both its composer.json branch and its explicit-version branch.

Verification

Public API and argument order are unchanged. Since these methods have no direct test coverage, I diffed old against new behavior over 14 cases through reflection on the resulting $sets: no arguments (composer.json resolution), php53/php74 by flag vs. by dedicated method, php80, php86, an explicitly-passed false, both downgrade targets, and all four throw paths (two versions at once, withPhpSets() called twice, no downgrade target, two downgrade targets). Output is byte-identical on every one.

Net -83 lines.