Refactor global variables

This aims to remove some of the annoying global structure which Stockfish has.

Overall there is no major elo regression to be expected.

Non regression SMP STC (paused, early version):
https://tests.stockfishchess.org/tests/view/65983d7979aa8af82b9608f1
LLR: 0.23 (-2.94,2.94) <-1.75,0.25>
Total: 76232 W: 19035 L: 19096 D: 38101
Ptnml(0-2): 92, 8735, 20515, 8690, 84

Non regression STC (early version):
https://tests.stockfishchess.org/tests/view/6595b3a479aa8af82b95da7f
LLR: 2.93 (-2.94,2.94) <-1.75,0.25>
Total: 185344 W: 47027 L: 46972 D: 91345
Ptnml(0-2): 571, 21285, 48943, 21264, 609

Non regression SMP STC:
https://tests.stockfishchess.org/tests/view/65a0715c79aa8af82b96b7e4
LLR: 2.94 (-2.94,2.94) <-1.75,0.25>
Total: 142936 W: 35761 L: 35662 D: 71513
Ptnml(0-2): 209, 16400, 38135, 16531, 193

These global structures/variables add hidden dependencies and allow data
to be mutable from where it shouldn't it be (i.e. options). They also
prevent Stockfish from internal selfplay, which would be a nice thing to
be able to do, i.e. instantiate two Stockfish instances and let them
play against each other. It will also allow us to make Stockfish a
library, which can be easier used on other platforms.

For consistency with the old search code, `thisThread` has been kept,
even though it is not strictly necessary anymore. This the first major
refactor of this kind (in recent time), and future changes are required,
to achieve the previously described goals. This includes cleaning up the
dependencies, transforming the network to be self contained and coming
up with a plan to deal with proper tablebase memory management (see
comments for more information on this).

The removal of these global structures has been discussed in parts with
Vondele and Sopel.

closes https://github.com/official-stockfish/Stockfish/pull/4968

No functional change

src/tune.cpp

@@ -24,14 +24,15 @@
 #include <sstream>
 #include <string>
 
-#include "uci.h"
+#include "ucioption.h"
 
 using std::string;
 
 namespace Stockfish {
 
 bool                              Tune::update_on_last;
-const UCI::Option*                LastOption = nullptr;
+const Option*                     LastOption = nullptr;
+OptionsMap*                       Tune::options;
 static std::map<std::string, int> TuneResults;
 
 string Tune::next(string& names, bool pop) {
@@ -53,13 +54,13 @@ string Tune::next(string& names, bool pop) {
     return name;
 }
 
-static void on_tune(const UCI::Option& o) {
+static void on_tune(const Option& o) {
 
     if (!Tune::update_on_last || LastOption == &o)
         Tune::read_options();
 }
 
-static void make_option(const string& n, int v, const SetRange& r) {
+static void make_option(OptionsMap* options, const string& n, int v, const SetRange& r) {
 
     // Do not generate option when there is nothing to tune (ie. min = max)
     if (r(v).first == r(v).second)
@@ -68,8 +69,8 @@ static void make_option(const string& n, int v, const SetRange& r) {
     if (TuneResults.count(n))
         v = TuneResults[n];
 
-    Options[n] << UCI::Option(v, r(v).first, r(v).second, on_tune);
-    LastOption = &Options[n];
+    (*options)[n] << Option(v, r(v).first, r(v).second, on_tune);
+    LastOption = &((*options)[n]);
 
     // Print formatted parameters, ready to be copy-pasted in Fishtest
     std::cout << n << "," << v << "," << r(v).first << "," << r(v).second << ","
@@ -79,13 +80,13 @@ static void make_option(const string& n, int v, const SetRange& r) {
 
 template<>
 void Tune::Entry<int>::init_option() {
-    make_option(name, value, range);
+    make_option(options, name, value, range);
 }
 
 template<>
 void Tune::Entry<int>::read_option() {
-    if (Options.count(name))
-        value = int(Options[name]);
+    if (options->count(name))
+        value = int((*options)[name]);
 }
 
 // Instead of a variable here we have a PostUpdate function: just call it