Refuse InternTable array keys that are too long to encode

Encoding an array key added each element's size to a running length
with unchecked arithmetic, and wrote into a fixed stack buffer whenever
the sum fit. A sparse array with a large length (2^29 elements or more)
wrapped the sum on 32-bit targets, so the write landed before the buffer;
on every target the encoder also visited every index of such an array.

Array keys now have at most 65536 elements, and their encoding at most
2^31 - 1 bytes. The size is computed first with sums that cannot wrap,
the buffer is sized to it, and keys over either limit make the lookup or
insert throw a TypeError before anything is read or written. The Node.js
implementation throws the same TypeError for keys of more than 65536
elements. Sparse elements are walked in one pass in index order, and the
index growth computation checks its size arithmetic too.

docs/content/docs/experimental.mdx

@@ -159,7 +159,7 @@ worker: square: 4 lines, 3 shapes
 
 <dl>
   <dt><code>new InternTable&lt;K, V&gt;(name)</code></dt>
-  <dd>Opens the table called <code>name</code>. Within one thread every construction with the same name refers to the same table. In scriptc builds every thread of the process shares it; under Node.js each thread has its own. Keys are strings, numbers, or arrays of numbers or of strings. Strings and numbers compare like <code>Map</code> keys; arrays compare by their elements in the same way.</dd>
+  <dd>Opens the table called <code>name</code>. Within one thread every construction with the same name refers to the same table. In scriptc builds every thread of the process shares it; under Node.js each thread has its own. Keys are strings, numbers, or arrays of numbers or of strings. Strings and numbers compare like <code>Map</code> keys; arrays compare by their elements in the same way and can have at most 65536 elements.</dd>
   <dt><code>table.get(key)</code>, <code>table.has(key)</code>, <code>table.size</code></dt>
   <dd>Read the table.</dd>
   <dt><code>table.getOrInsert(key, value)</code></dt>