fixes#18367fixes#21222
1. In vmdef.nim:304, newCtx now sets templInstCounter: new int when it
builds TCtx.
2. vm.nim:1490 — During VM execution of templates, c.templInstCounter is
passed to evalTemplate
3. evaltempl.nim:204 — instID: instID[] dereferences the ref int
4. With a nil templInstCounter, this would crash
5. The same initialization already exists on the semantic side in
sem.nim:787, so this change makes the VM path consistent with the rest
of the compiler.
(cherry picked from commit 67707a54b5)
