[web_compilers] Add support for js_interop_unsafe

[kevmoo]

Also bump min SDK
Also prepare for release

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• I’ve reviewed the contributor guide and applied the relevant portions to this PR.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:build_web_compilers	4.0.7	ready to publish	build_web_compilers-v4.0.7
package:build_test	2.2.2-wip	WIP (no publish necessary)
package:build_resolvers	2.4.1	already published at pub.dev
package:build_runner_core	7.2.12-wip	WIP (no publish necessary)
package:build_daemon	4.0.1	already published at pub.dev
package:build	2.4.2-wip	WIP (no publish necessary)
package:build_modules	5.0.5	already published at pub.dev
package:build_runner	2.4.7-wip	WIP (no publish necessary)
package:build_config	1.1.2-wip	WIP (no publish necessary)
package:scratch_space	1.0.3-wip	WIP (no publish necessary)

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:build_web_compilers	4.0.7	ready to publish	build_web_compilers-v4.0.7
package:build_test	2.2.2-wip	WIP (no publish necessary)
package:build_resolvers	2.4.1	already published at pub.dev
package:build_runner_core	7.2.12-wip	WIP (no publish necessary)
package:build_daemon	4.0.1	already published at pub.dev
package:build	2.4.2-wip	WIP (no publish necessary)
package:build_modules	5.0.5	already published at pub.dev
package:build_runner	2.4.7-wip	WIP (no publish necessary)
package:build_config	1.1.2-wip	WIP (no publish necessary)
package:scratch_space	1.0.3-wip	WIP (no publish necessary)

Documentation at https://github.com/dart-lang/ecosystem/wiki/Publishing-automation.