Add multi-line text truncation utilities (line-clamp)

[Atibayounus]

Description

Adds a new .line-clamp-{n} utility class (for n = 1 to 5) that truncates multi-line text using -webkit-line-clamp, similar to how the existing .text-truncate utility handles single-line truncation.

Usage:

<p class="line-clamp-3">Long text that will be truncated after 3 lines...</p>

Motivation & Context

Multi-line text truncation is commonly needed in cards, product descriptions, article previews, and responsive layouts. Currently, developers need to write custom CSS for this behavior. This utility provides a consistent, reusable solution built into Bootstrap.

Type of changes

• New feature (non-breaking change which adds functionality)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• N/A (docs not updated yet — this PR only adds the utility CSS/SCSS)

Related issues

Closes #42889

[Atibayounus]

Hi maintainers, (@julien-deramond )just following up on this PR. The required workflow checks are currently waiting for approval to run, and the PR needs a review from someone with write access before it can be merged. Could someone please approve the pending workflows and take a look at this when you get a chance? Thanks!