[clangd] Preserve qualified names in "override pure virtual methods" tweak (#163726)

Prevents the tweak from splitting **qualified names** (e.g.,
`foo::Type`) by incorrectly inserting a space around the scope
resolution (`::`).

**Before:**

```cpp
// input:
virtual foo::Type::func() = 0
// output:
foo :: Type :: func()
```

**After:**

```cpp
// input:
virtual foo::Type::func() = 0
// output:
foo::Type::func()
```
GitOrigin-RevId: 84a9ed25e816a51df765770e8867bccbde8da8e9