Add encaps var flags for AST_DIM/AST_VAR for php 8.2 (#227)

For https://wiki.php.net/rfc/deprecate_dollar_brace_string_interpolation

Closes #224

In util.php: Don't print a

Add encaps var flags for AST_DIM/AST_VAR for php 8.2 (#227)

For https://wiki.php.net/rfc/deprecate_dollar_brace_string_interpolation

Closes #224

In util.php: Don't print a 0 flag value for combinable flags

For php-ast self-testing, minimize the number of changes in the future
when similar combinable flags get added to existing ast var types.

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Support ast\flags\TYPE_FALSE for union types. (#140)

AST_CAST already has some impossible flags such as TYPE_ITERABLE.

This was overlooked when adding AST_TYPE_UNION

Support PHP 8.0 Union Type RFC