Shift Parser from 'Identifier' to 'Name' naming (#2947)

This PR renames parse nodes on a Name/NameExpression taxonomy. NameExpressions occur in a name context. The difference is that in non-expression contexts it's useful to return the identifier / string ID for adding to name lookup, whereas in expression contexts it's useful to return the resolved node ID for consistency with other expressions.

In the code, I do note SelfValueName is returned in the expression context: I'd expect this to change, as `self` in `[self: Self]` versus `self.Foo()` will probably be best handled similarly to the above. That means that, in the proposed taxonomy, both `SelfValueName` and `SelfValueNameExpression` will exist in order to assist semantics.

To contrast choices:

Original | Current | [zygoloid suggestion](https://discord.com/channels/655572317891461132/655578254970716160/1121581663399464970) | [This PR](https://discord.com/channels/655572317891461132/655578254970716160/1121814551789318215)
--- | --- | --- | ---
DeclaredName/DesignatedName | Identifier | NameComponent | Name
NameReference | NameReference | NameReference | NameExpression
SelfValueIdentifier | SelfValueIdentifier | SelfValueReference | SelfValueName
SelfTypeIdentifier | SelfTypeIdentiifer | SelfTypeReference | SelfTypeNameExpression

toolchain/parser/parser_handle_declaration_name_and_params.cpp

@@ -12,7 +12,7 @@ static auto ParserHandleDeclarationNameAndParams(ParserContext& context,
   auto state = context.PopState();
 
   if (!context.ConsumeAndAddLeafNodeIf(TokenKind::Identifier,
-                                       ParseNodeKind::Identifier)) {
+                                       ParseNodeKind::Name)) {
     CARBON_DIAGNOSTIC(ExpectedDeclarationName, Error,
                       "`{0}` introducer should be followed by a name.",
                       TokenKind);