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/parse/node_kind.h

@@ -52,7 +52,7 @@ class NodeKind : public CARBON_ENUM_BASE(NodeKind) {
 #define CARBON_PARSE_NODE_KIND(Name) CARBON_ENUM_CONSTANT_DECL(Name)
 #include "toolchain/parse/node_kind.def"
 
-  // Validates that a `parse_node_kind` parser node can be generated for a
+  // Validates that a `node_kind` parser node can be generated for a
   // `lex_token_kind` lexer token.
   auto CheckMatchesTokenKind(Lex::TokenKind lex_token_kind, bool has_error)
       -> void;