Everywhere: Use to_number<T> instead of to_{int,uint,float,double}

In a bunch of cases, this actually ends up simplifying the code as
to_number will handle something such as:

```
Optional<I> opt;
if constexpr (IsSigned<I>)
    opt = view.to_int<I>();
else
    opt = view.to_uint<I>();
```

For us.

The main goal here however is to have a single generic number conversion
API between all of the String classes.

Userland/Libraries/LibWeb/HTML/HTMLImageElement.cpp

@@ -176,7 +176,7 @@ unsigned HTMLImageElement::width() const
 
     // NOTE: This step seems to not be in the spec, but all browsers do it.
     auto width_attr = deprecated_get_attribute(HTML::AttributeNames::width);
-    if (auto converted = width_attr.to_uint(); converted.has_value())
+    if (auto converted = width_attr.to_number<unsigned>(); converted.has_value())
         return *converted;
 
     // ...or else the density-corrected intrinsic width and height of the image, in CSS pixels,
@@ -204,7 +204,7 @@ unsigned HTMLImageElement::height() const
 
     // NOTE: This step seems to not be in the spec, but all browsers do it.
     auto height_attr = deprecated_get_attribute(HTML::AttributeNames::height);
-    if (auto converted = height_attr.to_uint(); converted.has_value())
+    if (auto converted = height_attr.to_number<unsigned>(); converted.has_value())
         return *converted;
 
     // ...or else the density-corrected intrinsic height and height of the image, in CSS pixels,

Userland/Libraries/LibWeb/HTML/HTMLSelectElement.cpp

@@ -193,7 +193,7 @@ Optional<ARIA::Role> HTMLSelectElement::default_role() const
     if (has_attribute(AttributeNames::multiple))
         return ARIA::Role::listbox;
     if (has_attribute(AttributeNames::size)) {
-        auto size_attribute = deprecated_attribute(AttributeNames::size).to_int();
+        auto size_attribute = deprecated_attribute(AttributeNames::size).to_number<int>();
         if (size_attribute.has_value() && size_attribute.value() > 1)
             return ARIA::Role::listbox;
     }

Userland/Libraries/LibWeb/HTML/HTMLTableElement.cpp

@@ -46,7 +46,7 @@ void HTMLTableElement::visit_edges(Cell::Visitor& visitor)
 
 static unsigned parse_border(ByteString const& value)
 {
-    return value.to_uint().value_or(0);
+    return value.to_number<unsigned>().value_or(0);
 }
 
 void HTMLTableElement::apply_presentational_hints(CSS::StyleProperties& style) const

Userland/Libraries/LibWeb/HTML/Numbers.cpp

@@ -84,7 +84,7 @@ Optional<u32> parse_non_negative_integer(StringView string)
 Optional<double> parse_floating_point_number(StringView string)
 {
     // FIXME: Implement spec compliant floating point number parsing
-    auto maybe_double = MUST(String::from_utf8(string)).to_number<double>(TrimWhitespace::Yes);
+    auto maybe_double = string.to_number<double>(TrimWhitespace::Yes);
     if (!maybe_double.has_value())
         return {};
     if (!isfinite(maybe_double.value()))

Userland/Libraries/LibWeb/HTML/Parser/HTMLParser.cpp

@@ -4475,7 +4475,7 @@ RefPtr<CSS::StyleValue> parse_dimension_value(StringView string)
         number_string.append(*position);
         ++position;
     }
-    auto integer_value = number_string.string_view().to_int();
+    auto integer_value = number_string.string_view().to_number<int>();
 
     // 6. If position is past the end of input, then return value as a length.
     if (position == input.end())

Userland/Libraries/LibWeb/HTML/SourceSet.cpp

@@ -269,8 +269,8 @@ descriptor_parser:
         auto last_character = descriptor.bytes_as_string_view().bytes().last();
         auto descriptor_without_last_character = descriptor.bytes_as_string_view().substring_view(0, descriptor.bytes_as_string_view().length() - 1);
 
-        auto as_int = descriptor_without_last_character.to_int<i32>();
-        auto as_float = descriptor_without_last_character.to_float();
+        auto as_int = descriptor_without_last_character.to_number<i32>();
+        auto as_float = descriptor_without_last_character.to_number<float>();
 
         // - If the descriptor consists of a valid non-negative integer followed by a U+0077 LATIN SMALL LETTER W character
         if (last_character == 'w' && as_int.has_value()) {

Userland/Libraries/LibWeb/HTML/Window.cpp

@@ -235,7 +235,7 @@ static T parse_boolean_feature(StringView value)
         return T::Yes;
 
     // 4. Let parsed be the result of parsing value as an integer.
-    auto parsed = value.to_int<i64>();
+    auto parsed = value.to_number<i64>();
 
     // 5. If parsed is an error, then set it to 0.
     if (!parsed.has_value())