Fix gn (KhronosGroup#6131)

* no static initializers

Chromium bans static initializers of class objects.

Wrap the std::array static variables with a function
that returns a reference to them.
This is option 2 to remove static initializers, at
https://chromium.googlesource.com/chromium/src.git/+/HEAD/docs/static_initializers.md#Removing-Static-Initializers

Also, lookup methods update a pointer-to-const pointer.

* Fix GN build for ggt.py modules

Author: dneto0

BUILD.gn

@@ -49,6 +49,11 @@ action("spvtools_core_tables") {
     cldebuginfo100_insts_file,
     core_json_file,
     debuginfo_insts_file,
+    "utils/Table/__init__.py",
+    "utils/Table/Context.py",
+    "utils/Table/IndexRange.py",
+    "utils/Table/Operand.py",
+    "utils/Table/StringList.py",
   ]
   outputs = [
     core_tables_body_file,