Unbound type variable causes panic with RequiredTypeArguments and PatternSynonyms
The following example leads to a compiler panic:
```haskell
{-# LANGUAGE GADTs, RequiredTypeArguments, PatternSynonyms #-}
data T a where
MkT :: forall a -> T a
pattern P :: T a
pattern P = MkT (type a)
```
Reproducer constructed with assistance from Claude Opus 5.
GHC's error message is as follows:
```
Bug.hs:7:23: error: [GHC-76329]
• GHC internal error: ‘a’ is not in scope during type checking, but it passed the renamer
tcl_env of environment: [aoD :-> Type variable ‘a’ = a :: k,
asy :-> Type variable ‘k’ = k :: *]
• In the type ‘a’
In the expression: MkT (type a)
In an equation for ‘P’: P = MkT (type a)
|
7 | pattern P = MkT (type a)
| ^
```
The most likely cause is incorrect handling of `EmbTyPat` in `tcPatToExpr` in `compiler/GHC/Tc/TyCl/PatSyn.hs`.
issue