qapi: Enforce (or whitelist) case conventions on qapi members

We document that members of enums and objects should be
'lower-case', although we were not enforcing it. We have to
whitelist a few pre-existing entities that violate the norms.
Add three new tests to expose the new error message, each of
which first uses the whitelisted name 'UuidInfo' to prove the
whitelist works, then triggers the failure (this is the same
pattern used in the existing returns-whitelist.json test).

Note that by adding this check, we have effectively forbidden
an entity with a case-insensitive clash of member names, for
any entity that is not on the whitelist (although there is
still the possibility to clash via '-' vs. '_').

Not done here: a future patch should also add naming convention
support and whitelist exceptions for command, event, and type
names.

The additions to QAPISchemaMember.check_clash() check whether
info['name'] is in the whitelist (the top-most entity name at
the point 'info' tracks), rather than self.owner (the type,
possibly implicit, that directly owns the member), because it
is easier to maintain the whitelist by the names actually in
the user's .json file, rather than worrying about the names
of implicit types.

Backports commit 893e1f2c5170d54316f1dcf3fefae679175622fc from qemu

qemu/scripts/qapi.py

@@ -62,6 +62,20 @@ returns_whitelist = [
     'user_def_cmd3',
 ]
 
+# Whitelist of entities allowed to violate case conventions
+case_whitelist = [
+    # From QMP:
+    'ACPISlotType',         # DIMM, visible through query-acpi-ospm-status
+    'CpuInfoBase',          # CPU, visible through query-cpu
+    'CpuInfoMIPS',          # PC, visible through query-cpu
+    'CpuInfoTricore',       # PC, visible through query-cpu
+    'InputAxis',            # TODO: drop when x-input-send-event is fixed
+    'InputButton',          # TODO: drop when x-input-send-event is fixed
+    'QapiErrorClass',       # all members, visible through errors
+    'UuidInfo',             # UUID, visible through query-uuid
+    'X86CPURegister32',     # all members, visible indirectly through qom-get
+]
+
 enum_types = []
 struct_types = []
 union_types = []
@@ -1041,6 +1055,9 @@ class QAPISchemaMember(object):
 
     def check_clash(self, info, seen):
         cname = c_name(self.name)
+        if cname.lower() != cname and self.owner not in case_whitelist:
+            raise QAPIExprError(info,
+                                "%s should not use uppercase" % self.describe())
         if cname in seen:
             raise QAPIExprError(info,
                                 "%s collides with %s"