[Tolk] Get rid of ~tilda with mutate and self methods

This is a very big change.
If FunC has `.methods()` and `~methods()`, Tolk has only dot,
one and only way to call a `.method()`.
A method may mutate an object, or may not.
It's a behavioral and semantic difference from FunC.

- `cs.loadInt(32)` modifies a slice and returns an integer
- `b.storeInt(x, 32)` modifies a builder
- `b = b.storeInt()` also works, since it not only modifies, but returns
- chained methods also work, they return `self`
- everything works exactly as expected, similar to JS
- no runtime overhead, exactly same Fift instructions
- custom methods are created with ease
- tilda `~` does not exist in Tolk at all

tolk-tester/tests/var-apply.tolk

@@ -0,0 +1,22 @@
+fun getBeginCell() {
+    return beginCell;
+}
+
+fun getBeginParse() {
+    return beginParse;
+}
+
+@method_id(101)
+fun testVarApply1() {
+    var (_, f_end_cell) = (0, endCell);
+    var b: builder = (getBeginCell())().storeInt(1, 32);
+    b.storeInt(2, 32);
+    var s = (getBeginParse())(f_end_cell(b));
+    return (s.loadInt(32), s.loadInt(32));
+}
+
+fun main() {}
+
+/**
+@testcase | 101 |    | 1 2
+ */