Fix dropdown help icon layout

[LakshyaBagani]

Fixes #16838

Description
Fixed a layout issue where the help icon (?) for f:dropdownDescriptorSelector would intersect with the right border of the dropdown when used in constrained containers (like f:repeatableHeteroProperty).

The fix involves:

Reducing the dropdown width slightly (width: calc(100% - 3rem)) in
_select.scss.

Positioning the help icon in the newly created space (right: -2.5rem) in
_layout.scss.

This ensures the icon stays outside the field (avoiding overlap with the internal arrow/text) but remains within the overall footprint of the form item (avoiding intersection with the parent container's border).

Testing done
Manual verification was performed on a local Jenkins instance (2.548-SNAPSHOT):

• Navigated to the Global Tool Configuration page.
• Identified dropdowns with help icons.
• Verified that the help icon is correctly positioned outside the dropdown field.
• Verified that the help icon does not overlap with the dropdown arrow or selection text.
• Verified that the help icon does not bleed into the parent container's right border.

Screenshots (UI changes only)

Before

After

Proposed changelog entries
Fix help icon layout overlap for dropdownDescriptorSelector

Proposed changelog category
/label bug, web-ui

Proposed upgrade guidelines
N/A

Submitter checklist

• The issue, if it exists, is well-described.
• The changelog entries and upgrade guidelines are appropriate for the audience affected by the change (users or developers, depending on the change) and are in the imperative mood.
• There is automated testing or an explanation as to why this change has no tests. (Manual verification performed as this is a CSS layout fix).
• New public classes, fields, and methods are annotated with @restricted or have @SInCE TODO Javadocs, as appropriate.
• New deprecations are annotated with @deprecated(since = "TODO") or @deprecated(forRemoval = true, since = "TODO"), if applicable.
• UI changes do not introduce regressions when enforcing the current default rules of Content Security Policy Plugin.
• For dependency updates, there are links to external changelogs and, if possible, full differentials.
• For new APIs and extension points, there is a link to at least one consumer.

Desired reviewers
@timja @mawinter69 @MarkEWaite

[timja]

Please use the same before and after screenshots not different examples

[LakshyaBagani]

I have update the screenshots so that it refers to same example .

[LakshyaBagani]

@timja any updates regarding this PR ?

[LakshyaBagani]

Please let me know is this PR need any further change or not ?

[daniel-beck]

Fixed a layout issue where the help icon (?) for f:dropdownDescriptorSelector would intersect with the right border of the dropdown

This is not actually what the original issue is reporting. Is it obsolete and the problem has been fixed in the mean time?

[LakshyaBagani]

Fixed a layout issue where the help icon (?) for f:dropdownDescriptorSelector would intersect with the right border of the dropdown

This is not actually what the original issue is reporting. Is it obsolete and the problem has been fixed in the mean time?

Verified against latest master branch - the issue is still present and hasn't been fixed yet. The PR is still needed.