feature #14186 [Debug] Renamed "context" key to "scope_vars" to avoid any ambiguity (lyrixx)

This PR was merged into the 2.6 branch.

Discussion
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[Debug] Renamed "context" key to "scope_vars" to avoid any ambiguity

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | ~
| License       | MIT
| Doc PR        | ~

As seen with @nicolas-grekas ; the current key is ambiguous because the 2nd parameter in `Psr\LoggerInterface::info()` is already `context`. So when we "export" logs, it's confusing.

More over, now, the meaning is more accurate.

Commits
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b56a804 [Debug] Renamed "context" key to "scope_vars" to avoid any ambiguity

src/Symfony/Component/Debug/ErrorHandler.php

@@ -399,7 +399,7 @@ class ErrorHandler
 
         if ($type & $level) {
             if ($this->scopedErrors & $type) {
-                $e['context'] = $context;
+                $e['scope_vars'] = $context;
                 if ($trace) {
                     $e['stack'] = debug_backtrace(true); // Provide object
                 }