Fix floating point arguments being parsed as multiple parameters due to culture-specific formatting

[Copilot]

This PR fixes an issue where floating point arguments in [Arguments] attributes were incorrectly parsed as multiple parameters instead of single values, causing ArgumentException: Expected exactly 1 argument, but got 2 errors.

Root Cause

The issue occurred when floating point numbers were formatted using culture-specific decimal separators. In cultures like German (de-DE) and French (fr-FR), the decimal separator is a comma (,) instead of a period (.). This caused:

• 1.1 to be formatted as "1,1"
• The formatted string could then be mistakenly parsed as two separate arguments ["1", "1"]
• Tests would fail with "Expected exactly 1 argument, but got 2"

Example of the Issue

[Test]
[Arguments(1.1)]
[Arguments(0.1)] 
[Arguments(1e-1)]
public void ParameterTest(double number)
{
    // This would fail in de-DE culture with:
    // ArgumentException: Expected exactly 1 argument, but got 2
}

Solution

Updated three critical formatting methods to use CultureInfo.InvariantCulture for all numeric types:

1. TestNameFormatter.FormatArgumentValue() - Ensures test names display consistently
2. TypedConstantFormatter.FormatPrimitive() - Ensures source generator output is culture-independent
3. TypedConstantParser.FormatPrimitive() - Ensures argument parsing is culture-independent

The fix ensures that floating point numbers are always formatted with period (.) as the decimal separator, regardless of the user's locale settings.

Additionally, the emitted code now includes proper numeric type suffixes for clarity and correctness:

• d for double values (e.g., 1.1d)
• f for float values (e.g., 1.1f)
• m for decimal values (e.g., 1.23m)
• L for long values (e.g., 123L)
• UL for ulong values (e.g., 123UL)
• U for uint values (e.g., 123U)

Testing

Verified the fix works correctly across multiple cultures:

• English (US): 1.1 → "1.1d" ✅
• German (DE): 1.1 → "1.1d" ✅ (previously "1,1")
• French (FR): 1.1 → "1.1d" ✅ (previously "1,1")

All ArgumentsAttribute instances now correctly maintain exactly one argument value regardless of culture, and the emitted code includes proper numeric type suffixes.

Fixes #2961.

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[thomhurst]

@copilot We should still append the numeric representer in the emitted code. E.g. f for float, d for double

[Copilot]

@copilot We should still append the numeric representer in the emitted code. E.g. f for float, d for double

Added numeric suffixes to the emitted code: d for double, f for float, m for decimal, L for long, UL for ulong, and U for uint. Updated both TypedConstantFormatter and TypedConstantParser to ensure consistency. Source generator test snapshots have been updated to reflect the changes. (4085248)