Language Server Improvements: find references, basic autocompletion (c…

…hapel-lang#24213)

This PR implements a few extra features in the Python-based language
server.

* It adds `Scope` objects to the Python API. This makes it possible for
Python code to inspect scopes (currently, just listing used/imported
modules in a scope).
* It refactors the binary search code to be stored in a class, so that
other things (definitions) can be binary searched via cursor position.
* It uses the used/imported modules from the given file to provide
autocomplete suggestions for identifiers (currently not intelligent
enough to filter based on type / `bla.`).
* It builds another segment list for _defined_ symbols, and uses that
(and some additional bookkeeping) to find references _within a file_.

I'm planning on a refactor to keep track of workspace changes, so that
_global_ 'find references' works too.

Reviewed by @jabraham17 -- thanks!

## Testing
- [x] paratest for the parser changes

frontend/lib/parsing/ParserContext.h

@@ -329,7 +329,9 @@ struct ParserContext {
                                   bool isOverride);
 
   AstNode*
-  buildFormal(YYLTYPE location, Formal::Intent intent,
+  buildFormal(YYLTYPE location,
+              YYLTYPE locName,
+              Formal::Intent intent,
               PODUniqueString name,
               AstNode* typeExpr,
               AstNode* initExpr,
@@ -677,7 +679,9 @@ struct ParserContext {
   buildForwardingDecl(YYLTYPE location, owned<AttributeGroup> attributeGroup,
                       CommentsAndStmt cs);
 
-  AstNode* buildInterfaceFormal(YYLTYPE location, PODUniqueString name);
+  AstNode* buildInterfaceFormal(YYLTYPE location,
+                                YYLTYPE locName,
+                                PODUniqueString name);
 
   CommentsAndStmt buildInterfaceStmt(YYLTYPE location,
                                      PODUniqueString name,

frontend/lib/parsing/ParserContextImpl.h

@@ -1156,7 +1156,9 @@ ParserContext::buildFunctionExpr(YYLTYPE location, FunctionParts& fp) {
 }
 
 AstNode*
-ParserContext::buildFormal(YYLTYPE location, Formal::Intent intent,
+ParserContext::buildFormal(YYLTYPE location,
+                           YYLTYPE locName,
+                           Formal::Intent intent,
                            PODUniqueString name,
                            AstNode* typeExpr,
                            AstNode* initExpr,
@@ -1166,6 +1168,7 @@ ParserContext::buildFormal(YYLTYPE location, Formal::Intent intent,
   auto node = Formal::build(builder, loc, std::move(attr), name, intent,
                             toOwned(typeExpr),
                             toOwned(initExpr));
+  builder->noteDeclNameLocation(node.get(), convertLocation(locName));
   this->noteIsBuildingFormal(false);
   if (consumeAttributeGroup) resetAttributeGroupPartsState();
   return node.release();
@@ -3001,8 +3004,9 @@ ParserContext::buildSelectStmt(YYLTYPE location, owned<AstNode> expr,
 }
 
 AstNode* ParserContext::buildInterfaceFormal(YYLTYPE location,
+                                             YYLTYPE locName,
                                              PODUniqueString name) {
-  return buildFormal(location, Formal::Intent::TYPE, name,
+  return buildFormal(location, locName, Formal::Intent::TYPE, name,
                     /* typeExpr */ nullptr,
                     /* initExpr */ nullptr,
                     /* consumeAttributeGroup */ false);
@@ -3027,7 +3031,7 @@ CommentsAndStmt ParserContext::buildInterfaceStmt(YYLTYPE location,
     formalList = consumeList(formals);
   } else {
     auto selfStr = PODUniqueString::get(context(), "Self");
-    formalList.push_back(toOwned(buildInterfaceFormal(location, selfStr)));
+    formalList.push_back(toOwned(buildInterfaceFormal(location, {}, selfStr)));
   }
 
   AstList bodyStmts = bodyExprLst