This makes TokenizedBuffer more consistent with ParseTree and SemanticsIR, which also wrap with [] to produce a sequence value.
It also makes it possible in driver.cpp to just prefix the line with a name, so it ends up with:
var_name: [
(content)
]
Noticed this due to bracketing comments on #2443 and trying to think of better answers. With this, we can also say that the [] bracket a variable.
Jon Ross-Perkins
04f0288cd2