Added template-parameter-declaration-list

Committing an evening's work I've been meaning to do for a while... easier because a `<` `>` parameter list is just another parameter list (same parsing function, minor generalization).

Examples from the test case:

    f1: <T, U> (t:T, u:U) -> _ = {
        return t+u;
    }

    f2: <T:type, U:type> (t:T, u:U) -> _ = {
        return t+u;
    }

    f3: <T:_, U:_> () -> _ = {
        return T+U;
    }

    f4: <T: i8, U: i16> () -> _ = {
        return T+U;
    }

    main: () = {
        std::cout << "f1: (f1(1,1))$\n";
        std::cout << "f2: (f2(2,2))$\n";
        std::cout << "f3: (f3<3,3>())$\n";
        std::cout << "f4: (f4<4,4>())$\n";
    }

Author: hsutter

regression-tests/pure2-template-parameter-lists.cpp2

@@ -0,0 +1,23 @@
+
+f1: <T, U> (t:T, u:U) -> _ = {
+    return t+u;
+}
+
+f2: <T:type, U:type> (t:T, u:U) -> _ = {
+    return t+u;
+}
+
+f3: <T:_, U:_> () -> _ = {
+    return T+U;
+}
+
+f4: <T: i8, U: i16> () -> _ = {
+    return T+U;
+}
+
+main: () = {
+    std::cout << "f1: (f1(1,1))$\n";
+    std::cout << "f2: (f2(2,2))$\n";
+    std::cout << "f3: (f3<3,3>())$\n";
+    std::cout << "f4: (f4<4,4>())$\n";
+}

regression-tests/test-results/clang-12/pure2-template-parameter-lists.cpp.execution

@@ -0,0 +1,4 @@
+f1: 2
+f2: 4
+f3: 6
+f4: 8

regression-tests/test-results/clang-12/pure2-template-parameter-lists.cpp.output

@@ -0,0 +1,4 @@
+f1: 2
+f2: 4
+f3: 6
+f4: 8

regression-tests/test-results/gcc-10/pure2-template-parameter-lists.cpp.execution

@@ -25,7 +25,7 @@
     std::for_each(
         CPP2_UFCS_0(begin, view), 
         CPP2_UFCS_0(end, view), 
-        [](auto& x) {  return x += "-ish"; }
+        [](auto& x ) { return x += "-ish"; }
     );
 
     //  Initializating from a function expression

regression-tests/test-results/gcc-10/pure2-template-parameter-lists.cpp.output

@@ -0,0 +1,4 @@
+f1: 2
+f2: 4
+f3: 6
+f4: 8

regression-tests/test-results/mixed-function-expression-and-std-for-each.cpp

@@ -0,0 +1 @@
+pure2-template-parameter-lists.cpp

regression-tests/test-results/msvc-2022/pure2-template-parameter-lists.cpp.execution

@@ -0,0 +1,44 @@
+
+#define CPP2_USE_MODULES         Yes
+
+#include "cpp2util.h"
+
+
+#line 2 "pure2-template-parameter-lists.cpp2"
+template<typename T, typename U> [[nodiscard]] auto f1(T const& t, U const& u) -> auto;
+#line 6 "pure2-template-parameter-lists.cpp2"
+template<typename T, typename U> [[nodiscard]] auto f2(T const& t, U const& u) -> auto;
+#line 10 "pure2-template-parameter-lists.cpp2"
+template<auto T, auto U> [[nodiscard]] auto f3() -> auto;
+#line 14 "pure2-template-parameter-lists.cpp2"
+template<cpp2::i8 T, cpp2::i16 U> [[nodiscard]] auto f4() -> auto;
+#line 18 "pure2-template-parameter-lists.cpp2"
+auto main() -> int;
+
+//=== Cpp2 definitions ==========================================================
+
+#line 1 "pure2-template-parameter-lists.cpp2"
+
+template<typename T, typename U> [[nodiscard]] auto f1(T const& t, U const& u) -> auto{
+    return t + u; 
+}
+
+template<typename T, typename U> [[nodiscard]] auto f2(T const& t, U const& u) -> auto{
+    return t + u; 
+}
+
+template<auto T, auto U> [[nodiscard]] auto f3() -> auto{
+    return T + U; 
+}
+
+template<cpp2::i8 T, cpp2::i16 U> [[nodiscard]] auto f4() -> auto{
+    return T + U; 
+}
+
+auto main() -> int{
+    std::cout << "f1: " + cpp2::to_string(f1(1, 1)) + "\n";
+    std::cout << "f2: " + cpp2::to_string(f2(2, 2)) + "\n";
+    std::cout << "f3: " + cpp2::to_string(f3<3,3>()) + "\n";
+    std::cout << "f4: " + cpp2::to_string(f4<4,4>()) + "\n";
+}
+

regression-tests/test-results/msvc-2022/pure2-template-parameter-lists.cpp.output

@@ -0,0 +1,2 @@
+pure2-template-parameter-lists.cpp2... ok (all Cpp2, passes safety checks)
+