[IAST] Change filtered cookie vuln hash (DataDog#6032)

## Summary of changes
Update
[RFC](https://docs.google.com/document/d/1LLilcVkA1godL5sXuEoMlPFTT-hEF-8f-seGnx_CIvc/edit)
changes in filtered cookie calculation

## Reason for change
Previous option could collide with a cookie named `Filtered`

## Implementation details
Changed the hash calculation to `FILTERED_VULN` instead of
`VULN:Filtered`

## Test coverage
Added unit test

## Other details
<!-- Fixes #{issue} -->

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Author: daniel-romano-DD

tracer/src/Datadog.Trace/Iast/IastModule.cs

@@ -375,7 +375,7 @@ private static string BuildCommandInjectionEvidence(string file, string argument
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
     internal static int GetCookieHash(string vulnerability, string cookieName, bool isFiltered)
     {
-        return (vulnerability.ToString() + ":" + (isFiltered ? "Filtered" : cookieName)).GetStaticHashCode();
+        return (isFiltered ? ("FILTERED_" + vulnerability) : (vulnerability + ":" + cookieName)).GetStaticHashCode();
     }
 
     public static IastModuleResponse OnInsecureCookie(IntegrationId integrationId, string cookieName, bool isFiltered)

tracer/test/Datadog.Trace.Security.Unit.Tests/IAST/HashTests.cs

@@ -64,4 +64,16 @@ public void GivenAKownVulnerability_WhenCalculatedHash_ValueIsExpected(string vu
         var hashCode = vulnerability.GetHashCode();
         Assert.Equal(expectedHash, hashCode);
     }
+
+    [Theory]
+    [InlineData(VulnerabilityTypeName.InsecureCookie, "AspNetCoreRateLimit.RateLimitProcessor", false, -304624042)]
+    [InlineData(VulnerabilityTypeName.InsecureCookie, "AspNetCoreRateLimit.RateLimitProcessor", true, 990913114)]
+    [InlineData(VulnerabilityTypeName.InsecureCookie, "AspNetCore.Views_Iast_ReflectedXss+<<ExecuteAsync>b__8_1>d", true, 990913114)]
+    [InlineData(VulnerabilityTypeName.NoSameSiteCookie, "AspNetCore.Views_Iast_ReflectedXss+<<ExecuteAsync>b__8_1>d", false, 1003850134)]
+    [InlineData(VulnerabilityTypeName.NoSameSiteCookie, "AspNetCore.Views_Iast_ReflectedXss+<<ExecuteAsync>b__8_1>d", true, -636226626)]
+    [InlineData(VulnerabilityTypeName.NoSameSiteCookie, "AspNetCoreRateLimit.RateLimitProcessor", true, -636226626)]
+    public void GivenACookie_WhenCalculatedHash_ValueIsExpected(string vulnName, string cookieName, bool isFiltered, int hash)
+    {
+        IastModule.GetCookieHash(vulnName, cookieName, isFiltered).Should().Be(hash);
+    }
 }

tracer/test/snapshots/Iast.AspNetCore5.enableIast=True.path =_Iast_AllVulnerabilitiesCookie.verified.txt

@@ -47,63 +47,63 @@
     },
     {
       "type": "NO_SAMESITE_COOKIE",
-      "hash": -1837181716,
+      "hash": -636226626,
       "evidence": {
         "value": "LongCookie.abcdefghijklmnopqrstuvwxyz0123456789.0"
       }
     },
     {
       "type": "NO_HTTPONLY_COOKIE",
-      "hash": 1990393425,
+      "hash": -60481650,
       "evidence": {
         "value": "LongCookie.abcdefghijklmnopqrstuvwxyz0123456789.0"
       }
     },
     {
       "type": "INSECURE_COOKIE",
-      "hash": 1170867602,
+      "hash": 990913114,
       "evidence": {
         "value": "LongCookie.abcdefghijklmnopqrstuvwxyz0123456789.0"
       }
     },
     {
       "type": "NO_SAMESITE_COOKIE",
-      "hash": -1837181716,
+      "hash": -636226626,
       "evidence": {
         "value": "LongCookie.abcdefghijklmnopqrstuvwxyz0123456789.1"
       }
     },
     {
       "type": "NO_HTTPONLY_COOKIE",
-      "hash": 1990393425,
+      "hash": -60481650,
       "evidence": {
         "value": "LongCookie.abcdefghijklmnopqrstuvwxyz0123456789.1"
       }
     },
     {
       "type": "INSECURE_COOKIE",
-      "hash": 1170867602,
+      "hash": 990913114,
       "evidence": {
         "value": "LongCookie.abcdefghijklmnopqrstuvwxyz0123456789.1"
       }
     },
     {
       "type": "NO_SAMESITE_COOKIE",
-      "hash": -1837181716,
+      "hash": -636226626,
       "evidence": {
         "value": "LongCookie.abcdefghijklmnopqrstuvwxyz0123456789.2"
       }
     },
     {
       "type": "NO_HTTPONLY_COOKIE",
-      "hash": 1990393425,
+      "hash": -60481650,
       "evidence": {
         "value": "LongCookie.abcdefghijklmnopqrstuvwxyz0123456789.2"
       }
     },
     {
       "type": "INSECURE_COOKIE",
-      "hash": 1170867602,
+      "hash": 990913114,
       "evidence": {
         "value": "LongCookie.abcdefghijklmnopqrstuvwxyz0123456789.2"
       }