Don't use global variables in `scripts/package/node/core.js` and `core/utils/xml.ts`

[cpcallen]

Describe the bug

Due to the use of global variables to pass some (but not all) items obtained from the jsdom package from scripts/package/node/core.js to core/utils/xml.ts, XML serialisation (and therefore Blockly generally) is broken if:

1. Blockly is being loaded in node.js (or another runtime that does not have a native DOM implementation), and
2. more than one copy of Blocly is loaded.

Normally modules cannot be loaded more than once, but multiple copies of a module with different paths, or a single copy that is included in more than one (e.g. webpack) bundle, can defeat the usual deduping of loads to satisfy imports and requires.

Specifically, due to this bug, the @blockly/dev-scripts's test script, used by plugin developers (including us), is broken when used to test a project with more than one test/*.mocha.js test harness when using Blockly v9.2.0.

To Reproduce

Steps to reproduce the behavior:

1. Clone blockly-samples.
2. Choose any plugin with more than one test script in its test/ drirectory, where at least one of those tests creates a block.
3. Run npm upgrade blockly to bump blockly to 9.2.0.
4. Run npm test
5. Observe test errors.

Expected behaviour

Test should pass; no errors should occur.

Stack Traces

     TypeError: Failed to execute 'serializeToString' on 'XMLSerializer': parameter 1 is not of type 'Node'.
      at Object.exports.convert (webpack-internal:///./node_modules/jsdom/lib/jsdom/living/generated/Node.js:25:9)
      at XMLSerializer.serializeToString (webpack-internal:///./node_modules/jsdom/lib/jsdom/living/generated/XMLSerializer.js:111:23)
      at domToText$$module$build$src$core$utils$xml (webpack-internal:///./node_modules/blockly/blockly_compressed.js:74:333)

Additional context

See this lengthy discussion for more detail about the issue.

[cpcallen]

Proposed solution:

In utils/xml.ts

• Add one or more setters to utils/xml.ts to inject DOMParser, XMLSerializer or maybe the entire jsdom window object, and use the injected versions (defaulting to the browser-provided globals only if no other implementation is injected).
  • Do this in a way that is backward-compatible with the setDocument setter.
  • Consider doing so in a way that obviates the need for setDocument to be used at all, allowing it to be deprecated.
  • Consider marking new setters @internal.

In scripts/package/node/core.js:

• Call the new setter(s) to inject the jsdom-provided DOMParser and XMLSerializer functions ( or maybe the entire window object) to utils/xml.ts.
• Continue to set globalThis.DOMParser and globalThis.XMLSerializer, but include a wrapper noting they are deprecated. This is to avoid the change being a breaking change in the (perhaps unlikely) case that someone is using Blockly in node.js and has been relying on the versions of these functions we have been injecting into the global scope.

In a future major version, remove the code that modifies globalThis from scripts/package/node/core.js, and remove the setDocument setter from utils/xml.ts.