PSR2/SwitchDeclaration: remove dead code, bow out on parse errors

[ntdiary]

Description

• Bow out when a CASE/DEFAULT token is missing a scope opener or closer, avoiding undefined array key access.
• Remove the unreachable WrongOpener . $type fallback error message. The tokenizer can initially set a CASE/DEFAULT scope opener to T_COLON, T_SEMICOLON, T_CLOSE_TAG. The only exception is a braced block after the colon (case x: { ... }), where processAdditional() later reassigns the opener to T_OPEN_CURLY_BRACKET.
• Cache strtoupper($type) in $typeUc instead of calling it repeatedly.

Tests: rename the existing case file to SwitchDeclarationUnitTest.1.inc and add parse-error case files (.2.inc, .3.inc) verifying the sniff stays silent on broken switch statements.

Suggested changelog entry

• PSR2.ControlStructures.SwitchDeclarationSniff: prevent Undefined array key warnings when the sniff encounters a CASE/DEFAULT statement without a scope opener or closer (parse error / live coding).

Related issues/external references

Fixes #1472

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
  • This change is only breaking for integrators, not for external standards or end-users.
• Documentation improvement

PR checklist

• I have checked there is no other PR open for the same change.
• I have read the Contribution Guidelines.
• I grant the project the right to include and distribute the code under the BSD-3-Clause license (and I have the right to grant these rights).
• I have added tests to cover my changes.
• I have verified that the code complies with the projects coding standards.
• [Required for new sniffs] I have added XML documentation for the sniff.
• I have opened a sister-PR in the documentation repository to update the Wiki.