rustdoc-json: Add tests for statics

Author: aDotInTheVoid

Diff for: tests/rustdoc-json/statics/statics.rs

@@ -0,0 +1,10 @@
+//@ is '$.index[*][?(@.name=="A")].inner.static.type.primitive' '"i32"'
+//@ is '$.index[*][?(@.name=="A")].inner.static.is_mutable' false
+//@ is '$.index[*][?(@.name=="A")].inner.static.expr' '"5"'
+pub static A: i32 = 5;
+
+//@ is '$.index[*][?(@.name=="B")].inner.static.type.primitive' '"u32"'
+//@ is '$.index[*][?(@.name=="B")].inner.static.is_mutable' true
+// Expr value isn't gaurenteed, it'd be fine to change it.
+//@ is '$.index[*][?(@.name=="B")].inner.static.expr' '"_"'
+pub static mut B: u32 = 2 + 3;