Hold modifier keys on tap, double tap, and right click #399

Upstream: tester-army/e2e#957 (commit b1646e2, feat(agent): hold modifier keys on tap, double tap, and right click). Adds ctx.target.tapModifiers, executor/dispatcher/replay/trace-recorder changes, docs and agent-tap-modifiers.test.ts. The port has no tap modifiers yet.

Please evaluate and port.