Should initial double quotes in multiline strings always be escaped?

Currently, backslashes will be removed from escaped double quotes in multiline strings unless there are three or more together. Instead, maybe leading double quotes should always be escaped? The reason for possibly doing this is to reduce confusion when reading the code.

Currently:
```elm
x = """""a""b\"\"""" -- the string: ""a""b""
y = """"a"b\"""" -- the string: "a"b"
```

Proposed:
```elm
x = """\"\"a""b\"\"""" -- the string: ""a""b""
y = """\"a"b\"""" -- the string: "a"b"
```

No source file or test is named. Start by reproducing the two Elm multiline-string examples and compare the current behavior with the proposed escaping; done means the project has a decided behavior and verification for these cases.

Written by the indexing model from the issue text.