Add support for ScaleBar annotation

[mattpap]

TODO:

• finish vertical orientation
• two-dimensional scale bar
• support geographical projections (maps)
• finish the internal layout of the annotation
• move computational logic to Dimensional models
• make Dimensional models configurable
• add more predefined units and bases
• label/title alignment
• allow bar length in pixels
• allow bar decorations (e.g. tee head)
• add support for an exact mode
• add support math text (or at least unicode e.g. for um)
• add more examples
• add tests

Example:

scale_bar = ScaleBar(
    range=p.x_range,
    unit="mm",
    dimensional=MetricLength(), 
    orientation="horizontal",
    location="top_right",
    label_location="above",
    bar_length=0.2,
    bar_line_width=2,
    background_fill_alpha=0.8,
)

Note that displaying both a plain bar and an axis is just for the sake of the example and won't be the default.

This incorporates PR #13106.

fixes #11755

[codecov]

Codecov Report

Merging #13319 (831ae5a) into branch-3.3 (0bdaa42) will increase coverage by 0.02%.
Report is 5 commits behind head on branch-3.3.
The diff coverage is 100.00%.

@@              Coverage Diff               @@
##           branch-3.3   #13319      +/-   ##
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+ Coverage       92.44%   92.47%   +0.02%     
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  Files             317      318       +1     
  Lines           20264    20339      +75     
==============================================
+ Hits            18734    18809      +75     
  Misses           1530     1530              

[droumis]

@mattpap is this ready for review, given that geo projections and 2D will be in a different PR?

[mattpap]

is this ready for review, given that geo projections and 2D will be in a different PR?

Tentatively yes, but I'm still working on multiple issues.

[ianthomas23]

The appearance and zooming look really good.

There are rather a lot of properties of ScaleBar but I cannot see how to get rid of any of them, and I presume that default values will be fine for most use cases.

[mattpap]

There are rather a lot of properties of ScaleBar but I cannot see how to get rid of any of them, and I presume that default values will be fine for most use cases.

Which ones specifically? Many of those properties were "inherited" from Legend and ColorBar, and use the same default values. I've been considering to have a "bare" scale bar configurable in some way, i.e. no border, padding and background color and minimal spacing between its individual components.

[ianthomas23]

There are rather a lot of properties of ScaleBar ...

Which ones specifically? ...

None specifically, they all look useful and worth keeping. I was just commenting that there are lots of properties which might make use of ScaleBar intimidating to users. But no action is required on this.

[gmerritt123]

Amazing thanks so much for implementing this feature!