8343336: Add persistentScrollBars preference

[mstr2]

This PR adds another accessibility preference that is available on all supported desktop platforms:

1. Windows: Settings -> Accessibility -> Visual Effects -> Always show scroll bars
2. macOS: System Settings -> Appearance -> Show scroll bars
3. Ubuntu: Settings -> Accessibility -> Seeing -> Always show scroll bars

When the OS setting is changed, all platforms report updates that can be observed in JavaFX.
The manual test application test/manual/events/PlatformPreferencesChangedTest can be used to test the feature.

/reviewers 2
/csr

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Progress

• Change must not contain extraneous whitespace
• Commit message must refer to an issue
• Change requires CSR request JDK-8343451 to be approved
• Change must be properly reviewed (2 reviews required, with at least 1 Reviewer, 1 Author)

Issues

• JDK-8343336: Add persistentScrollBars preference (Enhancement - P4)
• JDK-8343451: Add persistentScrollBars preference (CSR)

Reviewing

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[bridgekeeper]

👋 Welcome back mstrauss! 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]

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

[openjdk]

@mstr2
The total number of required reviews for this PR (including the jcheck configuration and the last /reviewers command) is now set to 2 (with at least 1 Reviewer, 1 Author).

[openjdk]

@mstr2 has indicated that a compatibility and specification (CSR) request is needed for this pull request.

@mstr2 please create a CSR request for issue JDK-8343336 with the correct fix version. This pull request cannot be integrated until the CSR request is approved.

[mlbridge]

Webrevs

• 03: Full - Incremental (dc0eac58)
• 02: Full - Incremental (00de674f)
• 01: Full - Incremental (bd6ecbce)
• 00: Full (d37118cf)

[andy-goryachev-oracle]

This looks like a useful data point.

I am curious as to what are the criteria for including or excluding a particular preference? What is our long term goal - should we support all the preferences available on a particular platform, or the intersection, or what? May be it's something to discuss first on the mailing list.

[mstr2]

My thinking is that a particular preference should be useful and almost universally supported on the desktop platforms to make it into JavaFX API. The number of preferences we might consider are pretty limited, so I don't expect Platform.Preferences to explode in size and scope.

I think this is a minor addition that doesn't change anything substantial about Platform.Preferences, and as such doesn't need a major discussion since the arguments are basically the same since the introduction of platform preferences. However, if you or others are interested in having a discussion, we can of course do that.

[mstr2]

Changed the naming from reducedScrollBars to persistentScrollBars, as this matches the logic of the OS settings more closely.

[kevinrushforth]

My thinking is that a particular preference should be useful and almost universally supported on the desktop platforms to make it into JavaFX API.

This seems like the right criteria to me.

The number of preferences we might consider are pretty limited, so I don't expect Platform.Preferences to explode in size and scope.

Good.

I think this is a minor addition that doesn't change anything substantial about Platform.Preferences, and as such doesn't need a major discussion since the arguments are basically the same since the introduction of platform preferences. However, if you or others are interested in having a discussion, we can of course do that.

With this explanation, I agree.

[kevinrushforth]

Reviewers: @andy-goryachev-oracle @lukostyra

(I'll look over the public API and the CSR)

[kevinrushforth]

Do you also plan to add new platform-specific preferences or do you think this is unnecessary?

[mstr2]

I added the respective platform-specific keys to the Preferences documentation.