Use triple quotes in TOML.print when string contains newline (#55084)

closes #55083

Shouldu this also check for `\r`?

---------

Co-authored-by: Alex Arslan <ararslan@comcast.net>
(cherry picked from commit e732706)

stdlib/TOML/src/print.jl

@@ -101,9 +101,10 @@ function printvalue(f::MbyFunc, io::IO, value::TOMLValue, sorted::Bool)
     value isa AbstractFloat  ? Base.print(io, isnan(value) ? "nan" :
                                               isinf(value) ? string(value > 0 ? "+" : "-", "inf") :
                                               Float64(value)) :  # TOML specifies IEEE 754 binary64 for float
-    value isa AbstractString ? (Base.print(io, "\"");
+    value isa AbstractString ? (qmark = Base.contains(value, "\n") ? "\"\"\"" : "\"";
+                                Base.print(io, qmark);
                                 print_toml_escaped(io, value);
-                                Base.print(io, "\"")) :
+                                Base.print(io, qmark)) :
     value isa AbstractDict ? print_inline_table(f, io, value, sorted) :
     error("internal error in TOML printing, unhandled value")
 end

stdlib/TOML/test/print.jl

@@ -195,3 +195,13 @@ LocalPkg = {path = "LocalPkg"}
 """
 @test toml_str(d; sorted=true, inline_tables) == s
 @test roundtrip(s)
+
+# multiline strings (#55083)
+s = """
+a = \"\"\"lorem ipsum
+
+
+
+alpha\"\"\"
+"""
+@test roundtrip(s)