dictGet emulation with Variables

```
D SET VARIABLE my_map = MAP {'k1': 10, 'k2': 20};
D SELECT dictGet('my_map', 'k1');
```

chsql/src/chsql_extension.cpp

@@ -142,6 +142,9 @@ static DefaultMacro chsql_macros[] = {
     {DEFAULT_SCHEMA, "generateUUIDv4", {nullptr}, {{nullptr, nullptr}}, R"(toString(uuid()))"},
     {DEFAULT_SCHEMA, "parseURL", {"url", "part", nullptr}, {{nullptr, nullptr}}, R"(CASE part WHEN 'protocol' THEN REGEXP_EXTRACT(url, '^(\w+)://') WHEN 'domain' THEN REGEXP_EXTRACT(url, '://([^/:]+)') WHEN 'port' THEN REGEXP_EXTRACT(url, ':(\d+)') WHEN 'path' THEN REGEXP_EXTRACT(url, '://[^/]+(/.+?)(\?|#|$)') WHEN 'query' THEN REGEXP_EXTRACT(url, '\?([^#]+)') WHEN 'fragment' THEN REGEXP_EXTRACT(url, '#(.+)$') END)"},
     {DEFAULT_SCHEMA, "bitCount", {"num", nullptr}, {{nullptr, nullptr}}, R"(BIT_COUNT(num))"},
+    // Dictionary Emulation using MAP VARIABLES
+    {DEFAULT_SCHEMA, "dictGet", {"dict","attr", nullptr}, {{nullptr, nullptr}}, R"(getvariable(dict)[attr][1])"},
+    // -- End Macro
     {nullptr, nullptr, {nullptr}, {{nullptr, nullptr}}, nullptr}};
 
 // To add a new table SQL macro, add a new macro to this array!