Add configurable keyboard event routing

[satoshi-assistant]

Summary

• replace the key-only keyboard route list with explicit defaults for key events and accelerators
• add modifier-aware keyboard chords for wxp and native routing support in macOS/WebView2 backends
• keep child WebView parent-routed events from re-entering the wrapper before reaching the host view
• avoid unstable let-chain syntax in run_loop so the workspace builds on the current stable toolchain

Why

Embedded plugin UIs need WebView-owned shortcuts such as primary-modifier undo/redo to stay inside the WebView while selected host keys such as Space can still reach the parent host view. A key-only route list made that behavior ambiguous, especially for command-key paths on macOS.

Validation

• cargo fmt
• cargo check -p wry
• cargo check -p wxp
• cargo test -p wxp keyboard --lib
• cargo check -p wry --target x86_64-pc-windows-msvc
• cargo check -p wxp --target x86_64-pc-windows-msvc
• git diff --check