Support HTML5 drag-and-drop and drag modifier keys

[myabc]

What

Adds HTML5 native drag-and-drop and held modifier-key support to Node#drag_to, un-skipping the 15 Capybara shared drag specs that were previously force-skipped in spec/spec_helper.rb.

Why

Node#drag_to drove only real mouse events (move/down/move/up). Those never fire the HTML5 drag sequence (dragstart/dragover/drop/dragend + a DataTransfer), so any suite exercising HTML5 drag-and-drop had to fall back to Selenium.

Downstream motivation: opf/openproject#23218 currently switches to Selenium for its HTML5 drag-and-drop feature specs.

How

drag_to now routes between two paths after the initial mouse-down:

• Legacy path — the existing real-mouse drag, now applying held drop_modifiers via Ferrum's public mouse modifier bitfield (keyboard.modifiers + mouse.up(modifiers:)).
• HTML5 path — a JS emulation that dispatches the drag events with a shared DataTransfer, ported near-verbatim from Capybara's Selenium Html5Drag extension (HTML5_DRAG_DROP_SCRIPT). It lives in lib/capybara/cuprite/javascripts/drag.js and carries a header noting its provenance; it is kept close to the source (including a few inherited quirks) to ease future syncs.

Detection mirrors Capybara's LEGACY_DRAG_CHECK: the HTML5 path is taken when the source (or an ancestor) is draggable and the initial mousedown was not defaultPrevented; otherwise the legacy path runs.

Notes

• Uses only public Ferrum API — no raw CDP command() calls or reach-ins into Ferrum internals (per the direction in Cuprite 1.0 #307).
• Element#drop (files/strings/pathname) remains out of scope and is tracked separately.

Testing

• The 15 previously-skipped #drag_to specs (12 HTML5 + 3 mouse modifier) now pass.
• Full suite: no new failures versus main (the two #has_field validation-message failures are pre-existing and unrelated — Chrome locale wording).
• bundle exec rubocop clean.

Closes #314. Part of #307.

_{🤖 Authored with agent assistance.}

[Copilot]

Pull request overview

This PR adds HTML5-native drag-and-drop support (including DataTransfer + dragstart/dragover/drop/dragend sequencing) and held modifier-key support to Cuprite’s Node#drag_to, enabling previously force-skipped Capybara shared drag specs to run.

Changes:

• Unskips the previously skipped Capybara #drag_to specs in spec/spec_helper.rb.
• Extends Node#drag_to to accept drop_modifiers (with aliases) and routes through an updated browser drag command.
• Adds HTML5 drag emulation via injected JS (lib/capybara/cuprite/javascripts/drag.js) and runtime detection helpers in javascripts/index.js, with browser-side routing between legacy mouse drag vs HTML5 emulation.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
spec/spec_helper.rb	Removes forced skips so Capybara drag shared specs execute again.
lib/capybara/cuprite/node.rb	Adds drop_modifiers alias normalization and passes drag options to the browser command.
lib/capybara/cuprite/browser.rb	Implements legacy-vs-HTML5 routing, uses Ferrum mouse modifier bitfield on legacy path, and injects HTML5 drag emulation JS.
lib/capybara/cuprite/javascripts/index.js	Adds _cuprite helpers to track mousedown preventDefault and decide legacy vs HTML5 path.
lib/capybara/cuprite/javascripts/drag.js	New HTML5 drag event emulation script (ported approach) used by the HTML5 drag path.

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