Allow dynamic properties (e.g. endLineno) without deprecation notice in ast\Node

[TysonAndre]

(But use the default deprecation behavior for ast\Metadata)

1. php-ast itself sets the dynamic property on endLineno right now,
   causing deprecation notices in PHP 8.2.
   Because all declaration types are associative arrays(not lists),
   a future AST version number may add this as a property of
   $node->children instead to avoid this notice.

2. WeakMap is only available in PHP 8.0+ (and WeakReference 7.4),
   but https://github.com/phan/phan supports PHP 7.2+.

   Having a Phan version (or external plugins) that can work (and be fast) with a wider range of php versions is useful for organizations trying to detect uses of undeclared properties that need to migrate.

3. Because some nodes make $node->children a list,
   applications such as Phan using php-ast can't associate string keys
   with that.
   (e.g. to mark nodes that were already processed in a certain step)

   https://github.com/nikic/php-parser solves that by adding
   attributes, setAttribute, getAttribute, etc. separately from
   children, but php-ast currently doesn't currently have an attributes node.
   That may be useful to add (and to remove the AllowsDynamicProperty annotation in an incompatible php-ast major release)

   That may be worth it in a future release.

4. When processing a large number of ast nodes in a large number of
   files, the deprecation notices have a noticeable performance impact,
   even when suppressed.

Related to #214

Phan has a lot of uses of dynamic properties - e.g.

• to associate a hash with a node to check if two nodes are equivalent AST trees (probabalistically)
• to check (when using the polyfill fallback for php-ast) if syntax that's deprecated (unparenthesized ambiguous ?: syntax, trailing commas).
• to check if an AST node is already normalized to an easier to analyze form
• to check for infinite recursion
• to track information about a function's AST_STMT_LIST such as the set of used goto labels (can probably be migrated?)
• various others

src/Phan/AST/ASTHasher.php
66:        // @phan-suppress-next-line PhanUndeclaredProperty
67-        return $node->hash ?? ($node->hash = self::computeHash($node));

src/Phan/AST/TolerantASTConverter/TolerantASTConverter.php
1046:                    // @phan-suppress-next-line PhanUndeclaredProperty
1047-                    $result->is_not_parenthesized = true;
--
2096:            // @phan-suppress-next-line PhanUndeclaredProperty
2097-            $result->polyfill_has_trailing_comma = true;
--

[nikic]

Setting the flag explicitly should not be necessary.

[TysonAndre]

I tried removing the line. Deprecated: Creation of dynamic property ast\Node::$undeclaredDynamic is deprecated in /home/tyson/programming/php-ast/tests/php82_metadata.php on line 18 is the result.

This is the same as what https://github.com/php/php-src/blob/master/Zend/zend_builtin_functions.c does
at the time of writing:

https://github.com/php/php-src/blob/902d64390e49f8bf970588cf53cd8e00630c68bb/Zend/zend_builtin_functions.c#L39-L41

[nikic]

Ah yes, looks like the callback doesn't get called on interned classes for some reason.

[nikic]

Fine by me, allowing custom node extensions seems like a pragmatic choice.