fix(translator): correct trait composition precedence and alias modifiers

[AlessioGiacobbe]

Problem

Three defects in composeTraitAst diverge from PHP trait semantics:

1. A concrete method fulfilling another trait's abstract requirement is dropped (order-dependent):

trait NeedsName { abstract public function name(): string; }
trait HasName { public function name(): string { return "HasName"; } }
class C { use NeedsName, HasName; }   // valid PHP

The branch unsets the new concrete statement while the already-merged abstract one stays in the class AST, so the compiled class keeps only the abstract declaration → Cannot instantiate abstract class C at runtime. use HasName, NeedsName; (reverse order) works.

2. Alias adaptations wipe static/final/abstract:

trait Maker { public static function make(): string { return "made"; } }
class Factory { use Maker { make as protected; } }

$traitStmt->flags = $alias['newModifier'] replaces the whole flag set with just the visibility bits, so make loses static and compiles as an instance method. PHP replaces only the visibility bits (verified via Reflection: make as protected keeps isStatic(), and m as final keeps the original visibility).

3. A class-defined method doesn't suppress trait-vs-trait conflicts:

trait A { function who() { return "A"; } }
trait B { function who() { return "B"; } }
class C { use A, B; function who() { return "C"; } }   // valid PHP, class wins

dies with the spurious fatal Trait `B` method `who` already exists because the class-method check ran after conflict resolution, and suppressed trait copies were still registered as trait methods.

Fix

• Concrete-fulfills-abstract: drop the already-collected abstract declaration (from the class AST or the pending alias list) and keep the concrete method.
• New applyTraitAliasModifier(): a new visibility replaces only Modifiers::VISIBILITY_MASK bits; a modifier without visibility keeps the original one.
• The class-own-method check now runs before conflict resolution, and suppressed copies are not registered into $traitMethods.

Tests

• New tests/compiler/trait/trait-composition-precedence.phpt covers all three (both trait orders for the abstract case, alias visibility change with same and new name calling through static::, class method winning over two conflicting traits). Expected output verified against PHP 8.4.
• Full tests/compiler/trait/ suite: 41/41 pass. No new PHPStan errors on Translator.php.
• On master, the new test's scenarios fail with Trait `WhoB` method `who` already exists at compile time and, with that scenario removed, Cannot instantiate abstract class AbstractFirst at runtime.