Context variable overrides shared helper when hydratable: true

[mrkishi]

It seems having keys with the same name as shared helpers can cause problems in v1.57 SSR.

eg. This runs fine on the repl, but will error when SSRing because claim will try to call children:

https://svelte.technology/repl?version=1.57.0&gist=9a26ffaad3e8741640d51c55c1600ead

// (1:0) {{#if children}}
function create_if_block(component, state) {
	var ul;

	var children = state.children;

	var each_blocks = [];

	for (var i = 0; i < children.length; i += 1) {
		each_blocks[i] = create_each_block(component, assign({}, state, {
			children: children,
			child: children[i],
			child_index: i
		}));
	}

	return {
		c: function create() {
			ul = createElement("ul");

			for (var i = 0; i < each_blocks.length; i += 1) {
				each_blocks[i].c();
			}
		},

		l: function claim(nodes) {
			ul = claimElement(nodes, "UL", {}, false);
			var ul_nodes = children(ul); // <- children is not a function

			for (var i = 0; i < each_blocks.length; i += 1) {
				each_blocks[i].l(ul_nodes);
			}

			ul_nodes.forEach(detachNode);
		},