Open source TexasHoldem!

This change open sources the TexasHoldem game implementation.

Note: we're looking for folks who are interested to reproduce the Pluribus result to define certain aspects such as the informationState in such a way to effectively collapse states for computational efficiency.

Fixes #5

PiperOrigin-RevId: 266051344

swift/Tests/OpenSpielTests/XCTestManifests.swift

@@ -20,6 +20,8 @@ import XCTest
       testCase(BreakthroughTests.allTests),
       testCase(KuhnPokerTests.allTests),
       testCase(LeducPokerTests.allTests),
+      testCase(PokerDeckTests.allTests),
+      testCase(TexasHoldemTests.allTests),
       testCase(ExploitabilityTests.allTests),
       testCase(TicTacToeTests.allTests),
       testCase(GoPointTests.allTests),