AnalysisDriverFilesystem: add modificationStamp to _Resource.

[davidmorgan]

No description provided.

[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:build	2.4.2	already published at pub.dev
package:build_config	1.1.2	already published at pub.dev
package:build_daemon	4.0.3	already published at pub.dev
package:build_modules	5.0.11	already published at pub.dev
package:build_resolvers	2.4.4-wip	WIP (no publish necessary)
package:build_runner	2.4.15-wip	WIP (no publish necessary)
package:build_runner_core	8.0.1-dev	ready to publish	build_runner_core-v8.0.1-dev
package:build_test	2.2.4-wip	WIP (no publish necessary)
package:build_web_compilers	4.1.1	already published at pub.dev
package:scratch_space	1.0.3-wip	WIP (no publish necessary)

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

[github-actions]

PR Health