Interpolation wrapping breaks multi-line string indentation

[dduan]

A wrapped line inside a \(…) interpolation is not re-indented to the
multi-line string's indentation, so it ends up less-indented than the closing
""", producing source that no longer compiles.

Input

func test() {
  view {
    Button("Hi") {}
      .label(
        """
\(name: Color(
    .sRGBLinear, red: 1.0, green: 0.6, blue: 0.0))
""")
      .id("button")
  }
}

Output (invalid)

    Button("Hi") {}.label(
      """
      \(name: Color(
    .sRGBLinear, red: 1.0, green: 0.6, blue: 0.0))
      """
    ).id("button")

error: insufficient indentation of line in multi-line string literal — the
.sRGBLinear line (col 4) is less indented than the closing """ (col 6).

[allevato]

We were able to get away with punting on formatting interpolations at all for a long time because they're not allowed to be wrapped inside single-line strings. I guess we need to address this now if people are actually wrapping them inside multiline strings, where it is allowed.