allow setting inspectable in the theme

[aplavin]

Description

Fixes #4736 (issue)

Script to try:

using Pkg
pkg"activate --temp"
pkg"dev . ./GLMakie ./MakieCore"
using GLMakie
# set inspectable=false either in update_theme! of Figure:
# update_theme!(inspectable=false)
fig = Figure(inspectable=false)
# image() and first scatter() shouldn't be inspectable then:
image(fig[1,1], rand(3, 3))
scatter!(rand(10))
scatter!(rand(10), inspectable=true)
DataInspector(current_figure())
display(current_figure())
sleep(10)

Not sure if this change is testable with tests.

Type of change

Delete options that do not apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• Added an entry in CHANGELOG.md (for new features and breaking changes)

[aplavin]

Not sure why the benchmark job is failing, seems unrelated.
As for changelog, can easily add an entry if needed – depends on whether it's considered a bugfix or a new feature.