minor #3877 NamespacesAnalyzer - Optimize performance (stof)

This PR was merged into the 2.12 branch.

Discussion
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NamespacesAnalyzer - Optimize performance

Instead of looping on all tokens, even inside the namespace it identified, the analyzer now continues the analysis after the end of the identified namespace, thanks to the fact that namespaces cannot be nested.

When implementing #3876, I compared the NamespacesAnalyzer implementation with `\PhpCsFixer\Fixer\FunctionNotation\NativeFunctionInvocationFixer::getUserDefinedNamespaces`. The NamespacesAnalyzer also identifies the namespace name instead of skipping over it (and returns the global namespace too). But I found out that NativeFunctionInvocationFixer was more optimized, as it was not re-analyzing all tokens inside a namespace. This makes NamespacesAnalyzer implement the same optimization.

Commits
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8321c26 Optimize the namespaces analyzer

src/Tokenizer/Analyzer/NamespacesAnalyzer.php

@@ -29,7 +29,9 @@ public function getDeclarations(Tokens $tokens)
     {
         $namespaces = [];
 
-        foreach ($tokens as $index => $token) {
+        for ($index = 1, $count = \count($tokens); $index < $count; ++$index) {
+            $token = $tokens[$index];
+
             if (!$token->isGivenKind(T_NAMESPACE)) {
                 continue;
             }
@@ -57,6 +59,9 @@ public function getDeclarations(Tokens $tokens)
                 $index,
                 $scopeEndIndex
             );
+
+            // Continue the analysis after the end of this namespace to find the next one
+            $index = $scopeEndIndex;
         }
 
         if (0 === count($namespaces)) {