Automatically use alt text as title for images when no title is provided

[theletterf]

Fixes #1655

When adding images to documentation, users often need to specify sizing parameters (e.g., =50%) in the title attribute. This creates a redundancy issue where the alt text needs to be duplicated as the title before adding the size parameters, resulting in Markdown like:

![Description](/path/to/image.png "Description =50%")

This PR modifies the ImageBlock class to automatically use the alt text as the title value when no explicit title is provided. This allows users to:

1. Skip the redundant title text when only specifying size parameters:
   ![Description](/path/to/image.png "=50%")

2. Not have to duplicate information when using image directives.

Changes

• Modified the FinalizeAndValidate method in ImageBlock.cs to use alt text as the title when title is not specified
• Updated the documentation to explain this new behavior
• Updated test cases to reflect the new HTML output that includes title attributes

[github-actions]

🔍 Preview links for changed docs

• docs/syntax/images.md

[Mpdreamz]

Great QoL improvement 👍

[theletterf]

@Mpdreamz Looks like it's not working as intended. Looking at it.

[theletterf]

@Mpdreamz @reakaleek To make things simpler, I've made it so that Alt text always overrides the title, whether it's present or not. In most cases, the titles we have are not useful.

[florent-leborgne]

This is already super great! Is it possible to also check if the current title is plain "title" and in that case overwrite it with the alt value too? :D
Kind of a safety net

This could also be something we instead flag with a linter for example, if we don't want to bake it in docs-builder :)

Edit: nevermind, just saw your last comment @theletterf :D Perfect

[florent-leborgne]

This is greatttt

[Mpdreamz]

LGTM!