[Tolk] Rewrite the type system from Hindley-Milner to static typing

FunC's (and Tolk's before this PR) type system is based on Hindley-Milner.
This is a common approach for functional languages, where
types are inferred from usage through unification.
As a result, type declarations are not necessary:
() f(a,b) { return a+b; } // a and b now int, since `+` (int, int)

While this approach works for now, problems arise with the introduction
of new types like bool, where `!x` must handle both int and bool.
It will also become incompatible with int32 and other strict integers.
This will clash with structure methods, struggle with proper generics,
and become entirely impractical for union types.

This PR completely rewrites the type system targeting the future.
1) type of any expression is inferred and never changed
2) this is available because dependent expressions already inferred
3) forall completely removed, generic functions introduced
   (they work like template functions actually, instantiated while inferring)
4) instantiation `<...>` syntax, example: `t.tupleAt<int>(0)`
5) `as` keyword, for example `t.tupleAt(0) as int`
6) methods binding is done along with type inferring, not before
   ("before", as worked previously, was always a wrong approach)

tolk/symtable.cpp

@@ -17,28 +17,48 @@
 #include "symtable.h"
 #include "compiler-state.h"
 #include "platform-utils.h"
-#include <sstream>
-#include <cassert>
+#include "generics-helpers.h"
 
 namespace tolk {
 
+std::string FunctionData::as_human_readable() const {
+  if (!genericTs) {
+    return name;  // if it's generic instantiation like `f<int>`, its name is "f<int>", not "f"
+  }
+  return name + genericTs->as_human_readable();
+}
+
 bool FunctionData::does_need_codegen() const {
   // when a function is declared, but not referenced from code in any way, don't generate its body
   if (!is_really_used() && G.settings.remove_unused_functions) {
     return false;
   }
+  // functions with asm body don't need code generation
+  // (even if used as non-call: `var a = beginCell;` inserts TVM continuation inline)
+  if (is_asm_function() || is_builtin_function()) {
+    return false;
+  }
   // when a function is referenced like `var a = some_fn;` (or in some other non-call way), its continuation should exist
   if (is_used_as_noncall()) {
     return true;
   }
+  // generic functions also don't need code generation, only generic instantiations do
+  if (is_generic_function()) {
+    return false;
+  }
   // currently, there is no inlining, all functions are codegenerated
   // (but actually, unused ones are later removed by Fift)
   // in the future, we may want to implement a true AST inlining for "simple" functions
   return true;
 }
 
-void FunctionData::assign_is_really_used() {
-  this->flags |= flagReallyUsed;
+void FunctionData::assign_resolved_type(TypePtr declared_return_type) {
+  this->declared_return_type = declared_return_type;
+}
+
+void FunctionData::assign_inferred_type(TypePtr inferred_return_type, TypePtr inferred_full_type) {
+  this->inferred_return_type = inferred_return_type;
+  this->inferred_full_type = inferred_full_type;
 }
 
 void FunctionData::assign_is_used_as_noncall() {
@@ -49,14 +69,45 @@ void FunctionData::assign_is_implicit_return() {
   this->flags |= flagImplicitReturn;
 }
 
+void FunctionData::assign_is_type_inferring_done() {
+  this->flags |= flagTypeInferringDone;
+}
+
+void FunctionData::assign_is_really_used() {
+  this->flags |= flagReallyUsed;
+}
+
+void FunctionData::assign_arg_order(std::vector<int>&& arg_order) {
+  this->arg_order = std::move(arg_order);
+}
+
+void GlobalVarData::assign_resolved_type(TypePtr declared_type) {
+  this->declared_type = declared_type;
+}
+
 void GlobalVarData::assign_is_really_used() {
   this->flags |= flagReallyUsed;
 }
 
+void GlobalConstData::assign_resolved_type(TypePtr declared_type) {
+  this->declared_type = declared_type;
+}
+
 void LocalVarData::assign_idx(int idx) {
   this->idx = idx;
 }
 
+void LocalVarData::assign_resolved_type(TypePtr declared_type) {
+  this->declared_type = declared_type;
+}
+
+void LocalVarData::assign_inferred_type(TypePtr inferred_type) {
+#ifdef TOLK_DEBUG
+  assert(this->declared_type == nullptr);  // called when type declaration omitted, inferred from assigned value
+#endif
+  this->declared_type = inferred_type;
+}
+
 GNU_ATTRIBUTE_NORETURN GNU_ATTRIBUTE_COLD
 static void fire_error_redefinition_of_symbol(SrcLocation loc, const Symbol* previous) {
   SrcLocation prev_loc = previous->loc;