Fix parsing of awaited tagged template expressions

[rtsao]

Fixes #372

Before this, the parser would incorrectly parse await foo`bar` as Template(Await(...)) instead of Await(Template(...))

I assume LPrefix was used before because of the location of await in the precedence table (17), but it seems this doesn't match up with the observed behavior of other parsers.

In addition to tagged templates (with and without substitutions), I added test cases for await with both the lowest (comma) and highest (grouping and property access) operators.

[evanw]

Unfortunately I don't believe this is a valid fix for this issue. This change means await 1, 2 would be incorrectly parsed as await (1, 2) while it should be parsed as (await 1), 2 instead. This happens because changing LPrefix to LLowest here means "continue parsing all operators of any precedence after the await token".

Edit: One way to tell is to do await 1 == 1. That should be parsed as (await 1) == 1 but instead it's parsed as await (1 == 1) which esbuild prints as await true.