Add IsInline property support to FormCheckboxTagHelper

[Copilot]

This PR adds support for an IsInline property to the FormCheckboxTagHelper that allows checkboxes to be rendered horizontally instead of vertically stacked.

Changes Made

• Added IsInline boolean property to FormCheckboxTagHelper with a default value of false
• Enhanced CSS class building logic to append form-check-inline when IsInline is true
• Full compatibility with existing features like IsSwitch - you can now have inline switch checkboxes
• Comprehensive test coverage with 4 new tests covering all scenarios:
  • Default checkbox behavior
  • Inline checkbox behavior
  • Switch checkbox behavior
  • Inline switch checkbox behavior

Usage

<!-- Standard checkbox (vertical) -->
<form-checkbox asp-for="Item1"></form-checkbox>

<!-- Inline checkbox (horizontal) -->
<form-checkbox asp-for="Item2" is-inline="true"></form-checkbox>

<!-- Inline switch checkbox -->
<form-checkbox asp-for="Item3" is-inline="true" is-switch="true"></form-checkbox>

Visual Result

When IsInline="true" is set, the CSS class form-check-inline is added to the container div, making checkboxes display horizontally:

The screenshot shows the difference between:

• "Select Your Options" - Standard vertical checkboxes
• "Inline Options" - Horizontal inline checkboxes using is-inline="true"

Implementation Details

The implementation is minimal and follows the existing pattern used by the IsSwitch property. The CSS class building logic now includes:

if (IsInline)
{
    groupClass += " form-check-inline";
}

All 206 existing tests continue to pass, ensuring backward compatibility.

Fixes #55.

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