Update symfony/var-dumper requirement from ^3.3 to ^4.2

[dependabot-preview]

Updates the requirements on symfony/var-dumper to permit the latest version.

Changelog

Sourced from symfony/var-dumper's changelog.

CHANGELOG

4.3.0

• added DsCaster to support dumping the contents of data structures from the Ds extension

4.2.0

• support selecting the format to use by setting the environment variable VAR_DUMPER_FORMAT to html or cli

4.1.0

• added a ServerDumper to send serialized Data clones to a server
• added a ServerDumpCommand and DumpServer to run a server collecting
  and displaying dumps on a single place with multiple formats support
• added CliDescriptor and HtmlDescriptor descriptors for server:dump CLI and HTML formats support

4.0.0

• support for passing \ReflectionClass instances to the Caster::castObject()
  method has been dropped, pass class names as strings instead
• the Data::getRawData() method has been removed
• the VarDumperTestTrait::assertDumpEquals() method expects a 3rd $context = null
  argument and moves $message = '' argument at 4th position.
• the VarDumperTestTrait::assertDumpMatchesFormat() method expects a 3rd $context = null
  argument and moves $message = '' argument at 4th position.

3.4.0

• added AbstractCloner::setMinDepth() function to ensure minimum tree depth
• deprecated MongoCaster

2.7.0

• deprecated Cloner\Data::getLimitedClone(). Use withMaxDepth, withMaxItemsPerDepth or withRefHandles instead.

Commits

• 3c4084c Merge branch '3.4' into 4.2
• ca5fef3 Reword VarDumper description
• e760a38 minor #31133 [VarDumper] fix tests with ICU 64.1 (nicolas-grekas)
• dc84606 Merge branch '3.4' into 4.2
• cf7cbac [VarDumper] fix tests with ICU 64.1
• f088381 [VarDumper][Ldap] relax some locally failing tests
• f42850f Merge branch '3.4' into 4.2
• e463ad2 Optimize SVGs
• 9f87189 Merge branch '3.4' into 4.2
• d34d102 Apply php-cs-fixer rule for array_key_exists()
• Additional commits viewable in compare view

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[dependabot-preview]

Superseded by #13.