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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Add DIM_ALTERNATIVE_SYNTAX flag for 7.4's $x{$i}

Fixes #128

Fix ast\kind_uses_flags(ast\AST_ARROW_FUNC) in php < 7.4

Support FLAGS_COALESCE on AST_ASSIGN_OP (`??=`)