Open a new scope for static: expr blocks (#10649)

Bring this in line with how plain blocks are analysed and avoids codegen
errors if one references variables defined in such a block.

tests/errmsgs/tstaticexprscope.nim

@@ -0,0 +1,11 @@
+discard """
+  errmsg: "undeclared identifier: 'z'"
+  line: 11
+"""
+
+# Open a new scope for static expr blocks
+block:
+  let a = static:
+    var z = 123
+    33
+  echo z