[Violet] Fix for Swift 6.1 compatibility with Foundation.Expression.

[LiarPrincess]

Fix for #955 with Swift 6.1. Tested against swift-6.1-DEVELOPMENT-SNAPSHOT-2025-02-10-a-ubuntu24.04.

Failure

/build/swift-source-compat-suite/project_cache/violet/Sources/Compiler/Implementation/CompilerImpl+Expr.swift:14:31: error: 'Expression' is ambiguous for type lookup in this context
 12 | extension CompilerImpl {
 13 | 
 14 |   internal func visit(_ node: Expression) throws {
    |                               `- error: 'Expression' is ambiguous for type lookup in this context
 15 |     self.setAppendLocation(node)
 16 |     try node.accept(self)

Local run

➜  swift-source-compat-suite git:(main) ✗ ./runner.py \
  --swift-branch main \
  --projects projects.json \
  --include-actions 'action.startswith("Build")' \
  --include-repos 'path == "violet"' \
  --swiftc /home/michal/Downloads/swift-6.1-DEVELOPMENT-SNAPSHOT-2025-02-10-a-ubuntu24.04/usr/bin/swiftc


Building 1 projects across 4 parallel processes

UPASS: https://github.com/swiftlang/swift/issues/75499, violet, 5.3, 01693c, Swift Package
========================================
UPasses:
  UPASS: https://github.com/swiftlang/swift/issues/75499, violet, 5.3, 01693c, Swift Package
========================================
Action Summary:
     Passed: 0
     Failed: 0
    XFailed: 0
    UPassed: 1
      Total: 1
========================================
Repository Summary:
      Total: 1
========================================
Result: UPASS
========================================

[justice-adams-apple]

@swift-ci test

[justice-adams-apple]

@swift-ci test