Improve templates

### Issue description

As per https://github.com/dotnet/wpf/pull/6973#discussion_r958470912, we need to invert these conditions (https://github.com/dotnet/sdk/pull/27486) as we missed a version in the past:

```
"csharp9orOlder": {
"type": "generated",
"generator": "regexMatch",
"datatype": "bool",
"parameters": {
"pattern": "^(ISO-1|ISO-2|[1-7]|[8-9]|[8-9]\\.0|7\\.[0-3])$",
"source": "langVersion"
}
},
"csharp8orOlder": {
"type": "generated",
"generator": "regexMatch",
"datatype": "bool",
"parameters": {
"pattern": "^(ISO-1|ISO-2|[1-7]|8|8\\.0|7\\.[0-3])$",
"source": "langVersion"
}
},
"csharp7orOlder": {
"type": "generated",
"generator": "regexMatch",
"datatype": "bool",
"parameters": {
"pattern": "^(ISO-1|ISO-2|[1-7]|7\\.[0-3])$",
"source": "langVersion"
}
},

```