fix(resolver): stop corrupting single-segment `use const` imports

parseUse rebuilt the imported constant name by splitting on the last
backslash, but strrpos() returns false for a single-segment name:
`use const PHP_EOL;` registered the import as `\HP_EOL`
(substr($id, false + 1) drops the first character), and the compiled
program failed at runtime with `Undefined constant "HP_EOL"`.

$id is already the fully qualified constant name, so store it directly.
For multi-segment imports the removed recomposition produced the same
value, so their behavior is unchanged.

src/Resolver/DeclarationSymbolTrait.php

@@ -80,11 +80,11 @@ trait DeclarationSymbolTrait
             if ($type === Node\Stmt\Use_::TYPE_FUNCTION) {
                 $this->useFunctions[$alias] = $id;
             } elseif ($type === Node\Stmt\Use_::TYPE_CONSTANT) {
-                $lastIndex = strrpos($id, '\\');
+                // $id is already the fully qualified constant name. Splitting
-                $cn = substr($id, $lastIndex + 1);
+                // and re-joining it on `\` corrupted single-segment imports:
-                $ns = substr($id, 0, $lastIndex);
+                // `use const PHP_EOL;` resolved to `\HP_EOL` because
-                $fullName = $ns . '\\' . $cn;
+                // strrpos() returns false when there is no separator.
-                $this->useConstants[$alias] = $fullName;
+                $this->useConstants[$alias] = $id;
             } else {
                 $idLower = strtolower($id);
                 if ($idLower === 'native_types') {

tests/compiler/namespace/use-const-single-segment.phpt

@@ -0,0 +1,28 @@
+--TEST--
+use const with a single-segment (global) constant name
+--FILE--
+<?php
+namespace App {
+    use const PHP_EOL;
+
+    const ANSWER = 42;
+
+    function hello(): string
+    {
+        return "hello" . PHP_EOL;
+    }
+}
+
+namespace {
+    use const App\ANSWER;
+
+    function main(): void
+    {
+        echo \App\hello();
+        echo ANSWER, "\n";
+    }
+}
+?>
+--EXPECT--
+hello
+42