AK+LibPDF: Make Format print floats in a roundtrip-safe way by default

Previously we assumed a default precision of 6, which made the printed
values quite odd in some cases.
This commit changes that default to print them with just enough
precision to produce the exact same float when roundtripped.

This commit adds some new tests that assert exact format outputs, which
have to be modified if we decide to change the default behaviour.

AK/Format.h

@@ -238,15 +238,16 @@ public:
         SignMode sign_mode = SignMode::OnlyIfNeeded,
         RealNumberDisplayMode = RealNumberDisplayMode::Default);
 
-    ErrorOr<void> put_f64(
-        double value,
+    template<OneOf<f32, f64> T>
+    ErrorOr<void> put_f32_or_f64(
+        T value,
         u8 base = 10,
         bool upper_case = false,
         bool zero_pad = false,
         bool use_separator = false,
         Align align = Align::Right,
         size_t min_width = 0,
-        size_t precision = 6,
+        Optional<size_t> precision = {},
         char fill = ' ',
         SignMode sign_mode = SignMode::OnlyIfNeeded,
         RealNumberDisplayMode = RealNumberDisplayMode::Default);
@@ -265,6 +266,21 @@ public:
 
 private:
     StringBuilder& m_builder;
+
+#ifndef KERNEL
+    ErrorOr<void> put_f64_with_precision(
+        double value,
+        u8 base,
+        bool upper_case,
+        bool zero_pad,
+        bool use_separator,
+        Align align,
+        size_t min_width,
+        size_t precision,
+        char fill,
+        SignMode sign_mode,
+        RealNumberDisplayMode);
+#endif
 };
 
 class TypeErasedFormatParams {