StringLiterals and VariantKeys should not go though bundle._transform

[stasm]

I noticed this while working on #380. I'd like to discuss this in detail in the spec, but also fix this in a common-sense manner right now.

[Pike]

TBH, I would expect StringLiterals to go through pseudo localization.

I'm having formatToParts run around my head a lot, and I wonder if this would be the first thing to benefit from formatComplexPattern to be "to parts", and to move the transform into the bundle?

[stasm]

We'll need to discuss the details of how StringLiterals should be handled separately. I expect we'll want to exclude them from transform in cases like the following:

# "percent" should not be transformed.
string-literal-as-named-arg = {NUMBER(1, style: "percent")}

# "one" should not be transformed.
string-literal-as-selector = { "one" ->
    [one] One
   *[other] Other
}

# Not part of Fluent Syntax 1.0, but a possible addition in the future.
# "special key" should not be transformed.
string-litera-as-variant-key = { $var ->
    ["special key"] Special
   *[other] Other
}

Moreover, StringLiterals used as placeables already have the semantics of preserving the literal content from feratures like whitespace trimming.

trailing-whitespace = Foo{"         "}

It would make sense to me to extend this behavior to "protect" content from bundle._transform.

In the short term, I see disabling transforms for all StringLiterals as a good and safe starting position.

[stasm]

Fixed on the release branch in #394.