Format || patterns like fallthrough cases in switch expressions.

[munificent]

Switch statements allow multiple cases to share a body like:

switch (obj) {
  case pattern1:
  case pattern2:
    body;
}

Switch expressions don't support that, but || patterns are the idiomatic way to accomplish the same thing. Because of that, the formatter has some special formatting when the outermost pattern in a switch expression case is ||:

x = switch (obj) {
  pattern1 ||
  pattern2 =>
    body,
};

Note how the pattern2 operand isn't indented.

This PR extends that special handling to allow the => on the same line as the => even if the pattern is a split || pattern, like:

x = switch (obj) {
  pattern1 ||
  pattern2 => body,
};

And it prefers to split the || over the body when the body is block formatted:

// Prefer:
x = switch (obj) {
  pattern1 ||
  pattern2 => function(argument),
};

// Over:
x = switch (obj) {
  pattern1 || pattern2 => function(
    argument,
  ),
};

This is one of those rules that's mostly a matter of taste, but I ran this on a large corpus and most of the diffs look better to me. Here are a few examples:

// Before:
      typeName = switch (targetType) {
        DriftSqlType.int || DriftSqlType.bigInt || DriftSqlType.bool =>
          'INTEGER',
        DriftSqlType.string => 'CHAR',
        DriftSqlType.double => 'DOUBLE',
        DriftSqlType.blob => 'BINARY',
        DriftSqlType.dateTime => 'DATETIME',
        DriftSqlType.any => '',
        CustomSqlType() || DialectAwareSqlType() => targetType.sqlTypeName(
          context,
        ),
      };

// After:
      typeName = switch (targetType) {
        DriftSqlType.int ||
        DriftSqlType.bigInt ||
        DriftSqlType.bool => 'INTEGER',
        DriftSqlType.string => 'CHAR',
        DriftSqlType.double => 'DOUBLE',
        DriftSqlType.blob => 'BINARY',
        DriftSqlType.dateTime => 'DATETIME',
        DriftSqlType.any => '',
        CustomSqlType() ||
        DialectAwareSqlType() => targetType.sqlTypeName(context),
      };

// Before:
    return switch (side) {
      AxisSide.right || AxisSide.left =>
        titlesPadding.vertical + borderPadding.vertical,
      AxisSide.top || AxisSide.bottom =>
        titlesPadding.horizontal + borderPadding.horizontal,
    };

// After:
    return switch (side) {
      AxisSide.right ||
      AxisSide.left => titlesPadding.vertical + borderPadding.vertical,
      AxisSide.top ||
      AxisSide.bottom => titlesPadding.horizontal + borderPadding.horizontal,
    };

// Before:
    final defaultConstraints = switch (side) {
      ShadSheetSide.top || ShadSheetSide.bottom => BoxConstraints(
        minWidth: mSize.width,
      ),
      ShadSheetSide.left || ShadSheetSide.right => BoxConstraints(
        minHeight: mSize.height,
      ),
    };

    final defaultConstraints = switch (side) {
      ShadSheetSide.top ||
      ShadSheetSide.bottom => BoxConstraints(minWidth: mSize.width),
      ShadSheetSide.left ||
      ShadSheetSide.right => BoxConstraints(minHeight: mSize.height),
    };

Fix #1602.