Upgrading d3-cloud from 1.x to 2.x

See the [1.x to 2.x migration guide](./MIGRATING.md) before upgrading.
Dependencies constrained to 1.x continue to use the old API.

### Breaking

- Set the minimum Node.js version to 20, matching the CI test matrix.
- Switched the package to ESM-only publishing and removed the old Browserify /
  CommonJS distribution shape.
- Removed the UMD/script-tag build, the `d3.layout.cloud` global, and the
  `d3-dispatch` dependency. Browser scripts must use ESM imports.
- Changed the default rotation from random multiples of 30 degrees to zero,
  and the default font size from `sqrt(value)` to 1. Set styling explicitly.
- Input word objects are no longer mutated. Placement returns separate plain
  words, and callers control the word ordering.
- Custom data is carried in a single `datum` option, stored by reference on
  sprites and placed words. Other option fields are ignored rather than copied
  onto sprites and results, so built-in field names are no longer reserved.
- Replaced the old event-driven factory API (`start()`, `stop()`, `on()`,
  `words()`, `timeInterval()`, accessor-based text/font configuration) with the
  class-based `CloudLayout` / `CloudSprite` API.
- Replaced the old `spiral()` API with `strategy()`.
- Moved source files under `src/` and renamed the browser bundle to
  `build/d3-cloud.js`.
- Changed placement configuration so `size([width, height])` defines the
  centered layout box, while `overflow(true | false)` controls whether
  placement may extend beyond that box.
- Text padding now uses round stroke joins instead of the canvas default miter
  joins, so padding extends exactly `padding` pixels from the glyph outline
  rather than up to ten times that at sharp corners. Padded masks, and layouts
  that depend on them, differ from 1.x.
- The rectangular strategy now visits every point of a 4-pixel grid in rings
  shaped to the aspect ratio, instead of stepping four pixels times the aspect
  ratio along the longer axis. Rectangular layouts differ from 1.x, and pack
  densely at any aspect ratio.
- Both built-in spirals stretch to the aspect ratio only up to 64:1. Beyond
  that they barely moved along the shorter axis, so a search starting in a
  blocked column or row could take minutes and then fail. Layouts with more
  extreme aspect ratios differ from 1.x.
- Invalid arguments throw instead of being silently replaced: non-finite
  coordinates, sizes, rotations, padding, image dimensions and strategy
  candidates; negative padding; `size()` dimensions outside 0–16,777,216;
  `blockSize()` outside 1–4096; a `random()` that is not a function or returns
  anything but a number in `[0, 1)`; fonts the canvas rejects; canvases
  without a 2d context; and canvases whose `getImageData()` returns more than
  one pixel per canvas unit, as some old high-density WebKit canvases did.

### Added

- Added `CloudLayout.getSprite(...)` for explicit sprite preparation and
  `place()` for caller-controlled placement. Sprites are immutable masks with
 

Between d3-cloud 1.2.9 and 2.0.0, Vigia found 0 removed exports, 0 changed signatures and 0 removed or changed class or interface members.

0 exports or members are newly marked as deprecated in d3-cloud 2.0.0.