Update gradle lockfiles template

[bartekpacia]

This PR updates almost* all Gradle buildscripts in the Flutter repo the example and dev (in particular, in dev/integration_tests and in dev/benchmarks) directories to apply Flutter's Gradle plugins using the declarative plugins {} block.

*almost, because:

• add-to-app (aka hybrid) apps are not migrated (related Convert "module loader plugin" Gradle script into a proper Gradle plugin #138756)
• apps that purposefully use build files to ensure backward compatibility (e.g. gradle_deprecated_settings)

Pre-launch Checklist

• I read the [Contributor Guide] and followed the process outlined there for submitting PRs.
• I read the [Tree Hygiene] wiki page, which explains my responsibilities.
• I read and followed the [Flutter Style Guide], including [Features we expect every widget to implement].
• I signed the [CLA].
• I listed at least one issue that this PR fixes in the description above.
• I updated/added relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or this PR is [test-exempt].
• All existing and new tests are passing.

[bartekpacia]

Linux analyze is failing with a strange error. Rebasing multiple times didn't help.

[bartekpacia]

Rebasing again, let's see.

[reidbaker]

I am for this but I don't think we can just remove dependency locking as a feature in the framework.

[bartekpacia]

The dependency lockfiles that are removed by this PR are all buildscript-gradle.lockfile – that is, lockfiles that were locking only the buildscript dependencies. In other words, these lockfiles locked state of the buildscript.classpath configuration.

And since we're not using buildscript.classpath anymore, those lockfiles are not needed. I was searching the web for a way to create lockfiles for dependencies specified in the plugins {} block and found these 2 issues:

• Plugin dependency locks aren't generated for plugin block gradle/gradle#10437
• Dependency locking of settings classpath isn't properly persisted gradle/gradle#16593

[bartekpacia]

We'll need to generate settings-gradle.lockfile instead (e.g. with ./gradlew dependencies --write-locks?).

Investigating this now.

[auto-submit]

A reason for requesting a revert of flutter/flutter/140115 could
not be found or the reason was not properly formatted. Begin a comment with 'Reason for revert:' to tell the bot why
this issue is being reverted.

[bartekpacia]

Reason for revert: broke the tree

• Linux firebase_abstract_method_smoke_test
• Linux_android android_view_scroll_perf__timeline_summary
• Linux_android platform_views_scroll_perf__timeline_summary
• Linux_pixel_7pro platform_views_scroll_perf__timeline_summary
• Linux_pixel_7pro platform_views_scroll_perf_impeller__timeline_summary