Replace Perl binding cleanup with V on standard

[antono3]

Summary

• apply the V-native binding cleanup and variant-maintenance tooling to the standard ImGui line
• remove the combined Perl cleaner and the remaining Perl-backed maintenance scripts
• verify the standard upstream marker, generated layouts, and cleanup self-test in CI

Compatibility

This is the standard-branch counterpart to #27. The generated standard ImGui and ImPlot bindings reproduce the previous cleaner's output, apart from the implementation filename recorded in their non-regression note.

Verification

• v run cleanup_imgui_implot.vsh --self-test
• v vet cleanup_imgui_implot.vsh scripts/configure_variant.vsh scripts/check_upstream_variant.vsh generate.vsh
• v run scripts/check_upstream_variant.vsh reports Dear ImGui 1.92.9b standard
• v run generate.vsh completes translation, both cleanup passes, formatting, and native shared-library build
• post-regeneration worktree remains clean