Syntax highlighting when using a `lang-*` alias (and some "main" language codes) is broken

This issue doesn't seem to have anything to do with tags, especially since it's replicable here on MSE where virtually no language hints have a tag with the same name.

Instead, like you mentioned in your edit, it seems like we've got two distinct issues here:

1. Highlighting in post previews is broken, possibly because it wasn't updated to use the new rules now applied to actual, rendered posts.

   E.g. using lang-nonexistent on a post still produces highlighting in preview:

   

   Despite this not doing anything in rendered posts:

   console.log('Hello highlighter!');
   

2. Many aliases are now completely broken, and do not produce any highlighting. E.g., for JavaScript there are 5 aliases:

   lang-javascript, lang-js, (lang-jsx, lang-mjs, lang-cjs)

   But only the lang-js appears to actually work when posted:

   lang-javascript

   console.log('Hello highlighter!');
   

   lang-js

   console.log('Hello highlighter!');
   

   lang-jsx

   console.log('Hello highlighter!');
   

   lang-mjs

   console.log('Hello highlighter!');
   

   lang-cjs

   console.log('Hello highlighter!');
   

   Despite all of the above working in preview:

   

We've addressed the all the issues raised by kos & zcoop98 that were caused by updates in Stop guessing/auto-detecting a language when you KNOW it will be incorrect

1. We now exclude tags that aren't part of our predefined list of known good tags from highlighting in both preview and when rendered. This is somewhat tricky because we have two different MD -> HTML engines, one running in client-side running in JS, one in server-side running in C#.
2. We shored up the aliases used for each language block client and server side so they're the same.

Test Case 1 - Non Existent language tag

Input

```lang-nonexistant
var x = "123";
```

Output

var x = "123";

Test Case 2 - Supported Language Aliases

Input

```lang-js
var x = "123";
```

```lang-javascript
var x = "123";
```

```lang-bash
grep "pattern" filename.txt
```

```lang-sh
grep "pattern" filename.txt
```

Output

var x = "123";

var x = "123";

grep "pattern" filename.txt

grep "pattern" filename.txt

It should be noted that existing posts that have been affected by this bug need to be edited to have the fix - existing posts have not been re-rendered.

Thanks for reporting!