Support array literals in text_proto format

[Nick-Mazuk]

Currently, array literals are not parsed in the text_proto format.

For instance, consider the following message:

message Greetings {
    repeated string greetings = 1;
}

If you try to parse the following textproto with parse_from_str, you will get an error:

greetings: ["hello", "hi"]

ParseError { error: TokenizerError(ExpectStrLit), loc: Loc { line: 1, col: 12 } }

Instead, parse_from_str expects you to use string literals and repeat the field multiple times.

greetings: "hello"
greetings: "hi"

Array literals are valid in textproto format and should be supported.