Bug 245755 – [WGSL] Implement hex float parsing

• Status: NEW
• Component: WebGPU

[Dan Glastonbury]

WGSL doesn't support hex float parsing.

With a test, such as:

```
TEST(WGSLConstLiteralTests, AbstractFloatLiteralHex)
{
    const ConstLiteralTestCase<double> testCases[] = {
        { "0xa.fp+2"_s, 0xa.fp+2 },
        { "0X.3"_s, 0X.3p+0 },
        { "0X1.fp-4"_s, 0X1.fp-4 }
    };

    for (const auto& testCase : testCases) {
         auto parseResult = parseLCharPrimaryExpression(testCase.input);
         EXPECT_TRUE(parseResult);

         auto expr = WTFMove(*parseResult);
         EXPECT_TRUE(expr->isAbstractFloatLiteral());

         const auto& floatLiteral = downcast<WGSL::AST::AbstractFloatLiteral>(expr.get());
         EXPECT_EQ(floatLiteral.value(), testCase.expectedValue);
         auto inputLength = testCase.input.length();
         EXPECT_EQ(floatLiteral.span(), WGSL::SourceSpan(0, inputLength, inputLength, 0));
     }
}
```

[Radar WebKit Bug Importer]

<rdar://problem/100479770>