#123643
- Add task to projects evaluated by flutter.gradle that will print the
java version.
- Add integration test for the existence of javaVersion and the expected
format.
- Add gradle util to get the gradlew version for a specific platform
(gradlew everywhere but windows).

Why does this code need to exist? 
Figuring out what version of java is used by flutter/gradle is done in a
few different ways that are not always aligned.
See this issue https://github.com/flutter/flutter/issues/122609 ,
this issue https://github.com/flutter/flutter/issues/121501 this feature
request https://github.com/flutter/flutter/issues/106416

As examples of why assuming the java version is dangerous. 
This task is code flutter can build upon and is the version gradle is
using to build no matter how it is configured.



## Pre-launch Checklist

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

---------
Co-authored-by: Mitchell Goodwin <58190796+MitchellGoodwin@users.noreply.github.com>
Co-authored-by: Greg Spencer <gspencergoog@users.noreply.github.com>
Co-authored-by: Victoria Ashworth <vashworth@google.com>
Co-authored-by: Christopher Fujino <christopherfujino@gmail.com>
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