Fix parameter order

[the-fck]

The constructor for this specifies that after original_name comes position:

AstBase(const AstBase &ast, const char *original_name, size_t position = 0,
          size_t length = 0, size_t original_choice_count = 0,
          size_t original_choice = 0)

But in this case, choice_count came next.

[yhirose]

@the-fck thanks for the pull request. I don't fully understand what this pull request for. Could you explain more about this issue and provide a unit test for this pull request? Then, I'll start reviewing it. Thanks!

[the-fck]

@the-fck thanks for the pull request. I don't fully understand what this pull request for. Could you explain more about this issue and provide a unit test for this pull request? Then, I'll start reviewing it. Thanks!

Sure, I'm happy to better explain the fix here. In struct AstOptimizer, there is a spot where a new AST is constructed, but the parameters to that constructor do not match the expected order. Specifically, this leads to the position, length, and choice_count fields being incorrect in the new node. This PR moves the parameter original->choice_count to be in the expected location.