handlebars: Do not format html element attributes but class

[dcyriller]

Description

This PR stops formatting every html attributes for handlebars. Only class names will be formatted. This was breaking browser rendering and is considered a bug.

This would address #8667 (comment) (100% agreed).

TODO:

• We'll have to add formatting for style and srcset attributes later (similar to what html does).

Checklist

• I’ve added tests to confirm my change works.
• (If changing the API or CLI) I’ve documented the changes I’ve made (in the docs/ directory)
• (If the change is user-facing) I’ve added my changes to changelog_unreleased/*/pr-XXXX.md file following changelog_unreleased/TEMPLATE.md.
• I’ve read the contributing guidelines.

✨Try the playground for this PR✨

[fisker]

Should the attribute case insensitive?

Prettier pr-8677
Playground link

--parser glimmer

Input:

<A CLASS=" foo bar
          "></A>
<A class=" foo bar
          "></A>

Output:

<A CLASS=" foo bar
          " />
<A class="foo bar,[object Object]" />

Prettier pr-8677
Playground link

--parser html

Input:

<A CLASS=" foo bar
          "></A>
<A class=" foo bar
          "></A>

Output:

<a class="foo bar"></a> <a class="foo bar"></a>

[fisker]

@prettier/core Need review.

[kangax]

@dcyriller @fisker anything I can help with to get this merged? It's blocking the other PR that's also good to go.