Add utility classes for placeholder text alignment (logical start/end)

[RezaAmd]

Prerequisites

• I have searched for duplicate or closed feature requests
• I have read the contributing guidelines

Proposal

Add utility classes for aligning placeholder text independently from input text alignment, following Bootstrap’s logical property conventions.

This proposal introduces two new utility classes:

• .placeholder-start
• .placeholder-end

These utilities apply logical text alignment to the ::placeholder pseudo-element:

• start → aligns placeholder text to the inline start edge
• end → aligns placeholder text to the inline end edge

The proposed behavior mirrors existing text utilities such as text-start and text-end, but targets placeholder text specifically.

Example usage:

<input
  type="text"
  class="form-control text-start placeholder-end"
  placeholder="شماره تلفن"
/>

Motivation and context

In real-world form designs—especially in RTL interfaces—it is common to require different alignment rules for placeholder text and user-entered content.

A typical example is numeric or code-based inputs:

• The input value must be left-aligned (for readability and consistency)
• The placeholder text may need to be visually aligned to the opposite edge to match surrounding UI expectations

While CSS fully supports this use case via the ::placeholder pseudo-element, Bootstrap currently provides no utility-level solution to control placeholder alignment independently.

As a result, developers must fall back to custom CSS, which:

• Breaks consistency with Bootstrap’s utility-first approach
• Reduces reusability across projects
• Adds friction when working with mixed LTR/RTL layouts

This proposal aims to fill that gap by introducing a minimal, logical, and consistent utility API that:

• Aligns with Bootstrap’s existing start / end naming conventions
• Works seamlessly in both LTR and RTL contexts
• Improves real-world form UX without introducing physical (left/right) abstractions
• Avoids custom CSS for a common, valid use case

The proposed utilities are intentionally scoped, opt-in, and follow the same design principles as existing text and spacing utilities in Bootstrap.