[Admin] Solidus form builder

[chaimann]

Summary

Adds a convenient SolidusAdmin::FormBuilder with shortcuts for all currently used form elements, such as:

• raw input field
• text field (with labels etc.)
• hidden field
• text area
• select
• checkbox
• checkbox row
• switch field
• submit button

Before:

form_for(@product, ...) do |f|
  render component("ui/forms/field").text_field(f, :name)

After:

solidus_form_for(@product, ...) do |f|
  f.text_field(:name)

Lots of boilerplate code and logic is now contained in the builder, e.g. object name and "checked" attribute for checkboxes:

# before
form_for(@product, ...) do |f|
  render component("ui/forms/checkbox").new(object_name: f.object_name, method: :active, checked: f.object.active)

# after
solidus_form_for(@product, ...) do |f|
  f.checkbox(:active)

Submit button together with UI/Button's component #submit has now become a powerful "no-args-required" thing - component chooses a correct button text depending on a record passed to the form builder.
So this:

render component("ui/button").new(form: form_id, type: :submit, text: t('.submit')

becomes this:

f.submit

Checklist

Check out our PR guidelines for more details.

The following are mandatory for all PRs:

• I agree that my PR will be published under the same license as Solidus.
• I have written a thorough PR description.
• I have kept my commits small and atomic.
• I have used clear, explanatory commit messages.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.33%. Comparing base (da70045) to head (31952bb).
⚠️ Report is 28 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6294      +/-   ##
==========================================
+ Coverage   89.31%   89.33%   +0.02%     
==========================================
  Files         959      961       +2     
  Lines       20117    20157      +40     
==========================================
+ Hits        17968    18008      +40     
  Misses       2149     2149              

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[adammathys]

Love it. ❤️

[jarednorman]

I like this PR.

[benjaminwil]

Love this