Allow to customize toolbars with any UI components

[mattpap]

This is an early preview PR. This PR continues work started in PR #12417, by exposing the ability of configuring tool buttons instead of just tools to bokeh. It however expands on that work, allowing toolbar to include any UI elements (e.g. select boxes).

import numpy as np

from bokeh.plotting import figure, show
from bokeh.models import Toolbar, PaletteSelect
import bokeh.models.tools as t

N = 4000
x = np.random.random(size=N) * 100
y = np.random.random(size=N) * 100
radii = np.random.random(size=N) * 1.5
colors = np.array([(r, g, 150) for r, g in zip(50+2*x, 30+2*y)], dtype="uint8")

select = PaletteSelect(
    value="Red",
    items=[("Red", ["red"]), ("Green", ["green"]), ("Blue", ["blue"])],
    swatch_width=20,
)

children = [
    t.OnOffButton(tool=t.PanTool()),
    t.OnOffButton(tool=t.BoxSelectTool(persistent=True)),
    None,
    select,
    None,
    t.ClickButton(tool=t.ZoomInTool()),
    t.ClickButton(tool=t.ZoomOutTool()),
    None, # or Divider()
    t.ClickButton(tool=t.ResetTool()),
]

tb = Toolbar(children=children)
p = figure(toolbar=tb, toolbar_location="above", width=400, height=400)

p.circle(x, y, radius=radii, fill_color=colors, fill_alpha=0.6, line_color=None)
show(p)

Continues work on #8153, which was partially addressed by PR #13593.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.59%. Comparing base (e61219b) to head (109d1a8).
Report is 33 commits behind head on branch-3.5.

❗ Current head 109d1a8 differs from pull request most recent head 6ceb35e. Consider uploading reports for the commit 6ceb35e to get more accurate results

Additional details and impacted files

@@              Coverage Diff               @@
##           branch-3.5   #13571      +/-   ##
==============================================
+ Coverage       91.57%   92.59%   +1.01%     
==============================================
  Files             326      325       -1     
  Lines           20737    20744       +7     
==============================================
+ Hits            18990    19207     +217     
+ Misses           1747     1537     -210     

[mattpap]

A complete example (examples/basic/ui/toolbar_buttons_and_UIs.py) showing a toolbar with a custom button layout and a select widget (used for data filtering):

Screencast.from.18.02.2024.11.37.15.webm