Add control over layout scale bar unit position

[nyalldawson]

Description

Instead of forcing the units to always be placed after the last distance label, users now have a choice of exactly where they want them placed.

Options are:

• Vertically centered on the bar, before the bar begins
• Vertically centered on the bar, after the bar ends
• Text centered over the left edge of the bar, above the bar
• Horizontally centered on the bar, above the bar
• Text centered over the right edge of the bar, above the bar
• Text centered over the left edge of the bar, below the bar
• Horizontally centered on the bar, below the bar
• Text centered over the right edge of the bar, below the bar
• Placed before the first distance label
• Placed after the last distance label
• Placed on top of the bar, after the first bar division
• Placed before every distance label (as part of the distance label text)
• Placed after every distance label (as part of the distance label text)

Multiple options may be selected, allowing for fully flexible unit label positioning.

Sponsored by the QGIS Swiss User Group

AI tool usage

• Gemini was used to assist with text placement metrics

[qgis-bot]

@nyalldawson
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
Also, any commit having [needs-doc] or [Needs Documentation] in will see its message pushed to the issue, so please be as verbose as you can.

Thank you!

[qgis-bot]

@nyalldawson

This pull request has been tagged for the changelog.

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[github-actions]

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
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(Built from commit 17d8809)

🍎 MacOS Qt6 builds

Download MacOS Qt6 builds of this PR for testing.
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(Built from commit 17d8809)

[github-actions]

Tests failed for Qt 6 (ALL_BUT_PROVIDERS - ubuntu)

One or more tests failed using the build from commit 04d5fac

importComposerTemplateScaleBar_0 (importComposerTemplateScaleBar)

importComposerTemplateScaleBar_0

Test failed at importComposerTemplateScaleBar at tests/src/core/testqgscompositionconverter.cpp:487

Rendered image did not match tests/testdata/control_images/compositionconverter/expected_importComposerTemplateScaleBar_0/expected_importComposerTemplateScaleBar_0.png (found 215 pixels different)

importComposerTemplate_0 (importComposerTemplate)

importComposerTemplate_0

Test failed at importComposerTemplate at tests/src/core/testqgscompositionconverter.cpp:643

Rendered image did not match tests/testdata/control_images/compositionconverter/expected_importComposerTemplate_0/expected_importComposerTemplate_0.png (found 215 pixels different)

The full test report (included comparison of rendered vs expected images) can be found here.

Further documentation on the QGIS test infrastructure can be found in the Developer's Guide.

[github-actions]

Tests failed for Qt 6 (ALL_BUT_PROVIDERS - fedora)

One or more tests failed using the build from commit 04d5fac

importComposerTemplateScaleBar_0 (importComposerTemplateScaleBar)

importComposerTemplateScaleBar_0

Test failed at importComposerTemplateScaleBar at tests/src/core/testqgscompositionconverter.cpp:487

Rendered image did not match tests/testdata/control_images/compositionconverter/expected_importComposerTemplateScaleBar_0/expected_importComposerTemplateScaleBar_0.png (found 215 pixels different)

importComposerTemplate_0 (importComposerTemplate)

importComposerTemplate_0

Test failed at importComposerTemplate at tests/src/core/testqgscompositionconverter.cpp:643

Rendered image did not match tests/testdata/control_images/compositionconverter/expected_importComposerTemplate_0/expected_importComposerTemplate_0.png (found 215 pixels different)

The full test report (included comparison of rendered vs expected images) can be found here.

Further documentation on the QGIS test infrastructure can be found in the Developer's Guide.

[3nids]

shouldn't the space be preprended?