Fix LexicalLookupResult's node_id -> inst_id (#3476)

Noticed while working on #3475, but felt like it would be easy enough to
separate out.

toolchain/check/context.cpp

@@ -163,9 +163,9 @@ auto Context::AddNameToLookup(Parse::NodeId name_node, SemIR::NameId name_id,
  lexical_results.back().scope_index < current_scope_index())
  << "Failed to clean up after scope nested within the current scope";
  lexical_results.push_back(
- {.node_id = target_id, .scope_index = current_scope_index()});
+ {.inst_id = target_id, .scope_index = current_scope_index()});
  } else {
- DiagnoseDuplicateName(name_node, name_lookup_[name_id].back().node_id);
+ DiagnoseDuplicateName(name_node, name_lookup_[name_id].back().inst_id);
  }
 }
 
@@ -201,7 +201,7 @@ auto Context::LookupNameInDecl(Parse::NodeId parse_node, SemIR::NameId name_id,
  << "Should have been erased: " << names().GetFormatted(name_id);
  auto result = name_it->second.back();
  if (result.scope_index == current_scope_index()) {
- return result.node_id;
+ return result.inst_id;
  }
  }
  return SemIR::InstId::Invalid;
@@ -233,7 +233,7 @@ auto Context::LookupUnqualifiedName(Parse::NodeId parse_node,
  // it shadows all further non-lexical results and we're done.
  if (!lexical_results.empty() &&
  lexical_results.back().scope_index > index) {
- return lexical_results.back().node_id;
+ return lexical_results.back().inst_id;
  }
 
  auto non_lexical_result =
@@ -245,7 +245,7 @@ auto Context::LookupUnqualifiedName(Parse::NodeId parse_node,
  }
 
  if (!lexical_results.empty()) {
- return lexical_results.back().node_id;
+ return lexical_results.back().inst_id;
  }
 
  // We didn't find anything at all.

toolchain/check/context.h

@@ -400,9 +400,9 @@ class Context {
 
  // A lookup result in the lexical lookup table `name_lookup_`.
  struct LexicalLookupResult {
- // The node that was added to lookup.
- SemIR::InstId node_id;
- // The scope in which the node was added.
+ // The instruction that was added to lookup.
+ SemIR::InstId inst_id;
+ // The scope in which the instruction was added.
  ScopeIndex scope_index;
  };