Rename parse_node -> node_id (#3760)

This was previously discussed at
https://discord.com/channels/655572317891461132/655578254970716160/1209975051588210729.
I'm initiating this mainly because we typically use "id" suffixes to
indicate an `IdBase` being passed around and the non-id suffix of
`parse_node` suggests at it carrying more data than it actually does.
There used to be more reason for avoiding `node_id` because
`SemIR::InstId` used to be named `NodeId`, but that's no longer
necessary. As a consequence, I'd like to rename `parse_node` to more
precisely reflect its type.

In full, this is doing:

```
parse_node_kind -> node_kind
parse_node -> node_id
ParseNodeCategory -> NodeCategory
ParseNodeKind -> NodeKind
ParseNode -> NodeId
```

This is primarily in check and sem_ir, but with some `parse_node_kind`
references in parse too.

Pluralization is consistent with name forms on both sides, so that
wasn't part of my replacements.

toolchain/check/interface.cpp

@@ -29,7 +29,7 @@ auto BuildAssociatedEntity(Context& context, SemIR::InterfaceId interface_id,
   // not the declaration itself.
   auto type_id = context.GetAssociatedEntityType(
       interface_id, context.insts().Get(decl_id).type_id());
-  return context.AddInst({context.insts().GetParseNode(decl_id),
+  return context.AddInst({context.insts().GetNodeId(decl_id),
                           SemIR::AssociatedEntity{type_id, index, decl_id}});
 }