All HTMLAttrDef and HTMLAttrXRef macros are removed mdn/content

[schalkneethling]

From @OnkarRuikar

We've removed all HTMLAttrDef and HTMLAttrXRef macros from mdn/content. They've been converted to either markdown links or anchor tags. They are being marked deprecated in yari.

Henceforth use markdown style links or anchor tags:

a. For {{htmlattrxref("lang")}} use [lang](/en-US/docs/Web/HTML/Global_attributes#lang) in Markdown and
<a href="/en-US/docs/Web/HTML/Global_attributes#lang)"><code>lang</code></a> in HTML tables.
b. For {{htmlattrxref("srcset", "img")}} use [srcset](/en-US/docs/Web/HTML/Element/img#srcset) in Markdown <a href="/en-US/docs/Web/HTML/Element/img#srcset)"><code>srcset</code></a> in HTML tables.

The conversion was not as straightforward as I thought it would be. Thanks to @teoli2003, we solved the issues quickly.

Here is what we did:

1. Converted {{HTMLAttrDef("abc")}} to abc
2. Removed attr- from URL fragments /en-US/docs/Web/HTML/Element/tag#attr-abc
3. Converted HTMLAttrXRef macros:

a. Converted 1 argument instances to /en-US/docs/Web/HTML/Global_attributes#lang. Later we decided to convert these to /en-US/docs/Web/HTML/Global_attributes/lang (instead of a fragment, use the direct link)
b. Converted 3 and 4 argument instances. Because there was not a lot of these, I did it manually.
c. Converted 2 arg instances from {{HTMLAttrXref("attr", "tag")}} to [attr](/en-US/docs/HTML/Element/tag#attr).

1. We used [abc](#abc)
2. For same-page links, we had to use anchor tags for the instances in HTML tables: <a href="/en-US/../tag#attr)"><code>attr</code><a>

Note: Some macro instances were producing non-existing URLs because, over time, people put anything in the macro calls. Use PR assistants flaws section to find the broken URLs related to the task.

I used the following RegExes to semi-automate the task.

a. Convert 1 param macros:
Search: \{\{ ?htmlattrxref ?\( ?["']([^,]*?)["']\)\}\}
Replacement: [$1](/en-US/docs/Web/HTML/Global_attributes#$1)

b. Convert 2 param macros:
Search: \{\{ ?htmlattrxref ?\( ?["']([^,\n}]*?)["'], ?["']([^,\n}]*?)["']\)\}\}
Replacement: [$1](/en-US/docs/Web/HTML/Element/$2#$1)

Then to update markdown style links in HTML tables:
Search: (?<=<td>)(([\s\S](?!/td))*?)\[(.*)\]\((.*)\)
Replacement: $1<a href="$4"><code>$3</code></a>

[teoli2003]

A small nit:

Converted {{HTMLAttrDef("abc")}} to `abc`

[schalkneethling]

Thanks, @teoli2003 - updated.

[yin1999]

I found there are some cases that the macro are wrapped with inline-code. We may need to use regexp like \`?\{\{ ?htmlattrxref ?\( ?["']([^,]*?)["']\)\}\}\`? to avoid repeat wrapping.

[OnkarRuikar]

Also some old PRs that are getting merged now are re-introducing the macro instances to mdn/content.