LibWeb: Pass correct values to would_start_a_number()

This fixes the crash that Luke found using Domato:
```css
. foo {
    mso-border-alt: solid  .-1pt;
}
```

The spec distinguishes between "If the next 3 code points would
start..." and "If the input stream starts with..." but we were treating
them the same way, skipping the first code point in the process.

Userland/Libraries/LibWeb/CSS/Parser/Tokenizer.cpp

@@ -881,11 +881,6 @@ Token Tokenizer::consume_a_numeric_token()
     return token;
 }
 
-bool Tokenizer::would_start_a_number() const
-{
-    return would_start_a_number(peek_triplet());
-}
-
 // https://www.w3.org/TR/css-syntax-3/#starts-with-a-number
 bool Tokenizer::would_start_a_number(U32Triplet values)
 {
@@ -1189,7 +1184,7 @@ Token Tokenizer::consume_a_token()
         dbgln_if(CSS_TOKENIZER_DEBUG, "is plus sign");
         // If the input stream starts with a number, reconsume the current input code point,
         // consume a numeric token and return it.
-        if (would_start_a_number()) {
+        if (would_start_a_number(start_of_input_stream_triplet())) {
             reconsume_current_input_code_point();
             return consume_a_numeric_token();
         }
@@ -1210,7 +1205,7 @@ Token Tokenizer::consume_a_token()
         dbgln_if(CSS_TOKENIZER_DEBUG, "is hyphen minus");
         // If the input stream starts with a number, reconsume the current input code point,
         // consume a numeric token, and return it.
-        if (would_start_a_number()) {
+        if (would_start_a_number(start_of_input_stream_triplet())) {
             reconsume_current_input_code_point();
             return consume_a_numeric_token();
         }
@@ -1241,7 +1236,7 @@ Token Tokenizer::consume_a_token()
         dbgln_if(CSS_TOKENIZER_DEBUG, "is full stop");
         // If the input stream starts with a number, reconsume the current input code point,
         // consume a numeric token, and return it.
-        if (would_start_a_number()) {
+        if (would_start_a_number(start_of_input_stream_triplet())) {
             reconsume_current_input_code_point();
             return consume_a_numeric_token();
         }

Userland/Libraries/LibWeb/CSS/Parser/Tokenizer.h

@@ -101,7 +101,6 @@ private:
     [[nodiscard]] static bool is_valid_escape_sequence(U32Twin);
     [[nodiscard]] bool would_start_an_identifier();
     [[nodiscard]] bool would_start_an_identifier(U32Triplet);
-    [[nodiscard]] bool would_start_a_number() const;
     [[nodiscard]] static bool would_start_a_number(U32Triplet);
 
     String m_decoded_input;