tokenizer fails on an await expression containing a regexp

[ascidian]

Tokenizer fails the following test while the parser works fine.

async function f(){ await /a*/; }

It appears to interpret as { (await / a) * /;, } leading to an unterminated regexp error.

To reproduce:
node acorn/dist/bin.js --ecma2020 --tokenize <test-file.js>

[RReverser]

Note that tokenizer will never match what a full parser can, even though it's pretty close.

But in this instance, I think, we should be able to modify tokencontext.js to handle async-await in a similar way that it already handles generators & yield.