Parser swallows leading whitespace after indented placeable

[RumovZ]

In this fixture, the leading whitespace in front of "four" is preserved as expected:

key12 =
{ "." }
    four

However, with normalized indentation, it is not:

key12 =
    { "." }
        four

This is wrongly parsed to the same AST as this:

key12 =
    { "." }
    four

[gregtatum]

I'm tentatively marking this as a good first issue since it will probably be a relatively small patch, but you should probably like parsers if you want to take this one.

[RumovZ]

When this is fixed, crlf.ftl may be removed from the IGNORE_LIST in fluent-syntax/tests/serializer_fixtures.rs.