8240539: Upgrade gradle to version 6.3

[arapte]

jfx11u uses gradle 5.3 for build, it needs to be upgraded to gradle 6.3 same as jfx mainline.
This PR backports three fixes:

1. JDK-8240539: Upgrade gradle to version 6.3
2. JDK-8232063: Upgrade gradle to version 6.0 and
3. JDK-8226754: FX build fails using gradle 5.6+ or 6

All the changes backport cleanly.

---

Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change must be properly reviewed

Issues

• JDK-8240539: Upgrade gradle to version 6.3
• JDK-8232063: Upgrade gradle to version 6.0
• JDK-8226754: FX build fails using gradle 5.6+ or 6

Reviewers

• Kevin Rushforth (@kevinrushforth - Reviewer)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.java.net/jfx11u pull/7/head:pull/7
$ git checkout pull/7

Update a local copy of the PR:
$ git checkout pull/7
$ git pull https://git.openjdk.java.net/jfx11u pull/7/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 7

View PR using the GUI difftool:
$ git pr show -t 7

Using diff file

Download this PR as a diff file:
https://git.openjdk.java.net/jfx11u/pull/7.diff

[bridgekeeper]

👋 Welcome back arapte! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

[openjdk]

⚠️ @arapte could not find any commit with hash d7cab4a02169599043d0024faf62f92d90c48222. Please update the title with the hash for an existing commit.

[openjdk]

This backport pull request has now been updated with issue from the original commit.

[arapte]

/issue add JDK-8232063, JDK-8226754

[openjdk]

@arapte
Adding additional issue to issue list: 8232063: Upgrade gradle to version 6.0.

Adding additional issue to issue list: 8226754: FX build fails using gradle 5.6+ or 6.

[mlbridge]

Webrevs

• 00: Full (18433722)

[kevinrushforth]

Looks good.

[openjdk]

@arapte This change now passes all automated pre-integration checks.

ℹ️ This project also has non-automated pre-integration requirements. Please see the file CONTRIBUTING.md for details.

After integration, the commit message for the final commit will be:

8240539: Upgrade gradle to version 6.3
8232063: Upgrade gradle to version 6.0
8226754: FX build fails using gradle 5.6+ or 6

Reviewed-by: kcr

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been no new commits pushed to the master branch. If another commit should be pushed before you perform the /integrate command, your PR will be automatically rebased. If you prefer to avoid any potential automatic rebasing, please check the documentation for the /integrate command for further details.

➡️ To integrate this PR with the above commit message to the master branch, type /integrate in a new comment.

[arapte]

/integrate

[openjdk]

@arapte Since your change was applied there has been 1 commit pushed to the master branch:

• fdd0fa0: 8204568: Relative CSS-Attributes don't work all time

Your commit was automatically rebased without conflicts.

Pushed as commit 6ff7384.

💡 You may see a message that your pull request was closed with unmerged commits. This can be safely ignored.