[clang-tools-extra] [Clang-doc] Display enum comments in HTML (PR #183085)

[Samrudh Nelli via cfe-commits]

SamrudhNelli wrote:

```
<td>
{{#Description}}
<!-- whatever logic ... --->
{{/Description}}
{{^Description}} -- {{/Description}}
</td>
```
The problem with the above format is that for enums with a Description. a trailing new line will be added due to the {{^Description}} check. 

Current code:
```
<td>{{#Description}}
<!-- whatever logic ... --->
{{/Description}}
{{^Description}} -- {{/Description}}</td>
```
Alternative (Remove adding "--" for empty cells):
```
<td>
{{#Description}}
<!-- whatever logic ... --->
{{/Description}}
</td>
```

https://github.com/llvm/llvm-project/pull/183085