Issue 10133 - ICE for templated static conditional lambda

https://d.puremagic.com/issues/show_bug.cgi?id=10133

Currently template constraint is evaluated under the following nested scope:
```
TemplateDeclaration
  + FuncDeclaration (if exists)
     + constraint
```

But this is very special hierarchy, because normally `TemplateDeclaration` does not appear in symbol tree. This PR changes it to:

```
TemplateInstance  (artificially made)
  + FuncDeclaration (artificially made, if exists)
     + constraint
```

by emulating template instantiation.