[api-merge] Update "constant" values if they change between API levels.

[jpobst]

Context: #9000

In #9000, we learned that:

• Constant values can change between Android API levels
• api-merge does not update constant values in the final api.xml if they do change

Update api-merge to update constant values if they change, and update api-VanillaIceCream.xml with the new api-merge logic.

[jpobst]

With this updated api-VanillaIceCream.xml, the only reported constant mismatch is the one reported in #9000, which was caused by an error in our enumification process:

Mismatch: android/app/ApplicationExitInfo.REASON_OTHER 10 != 13 [API-30]

[jonpryor]

Draft commit message:

Context: https://github.com/xamarin/xamarin-android/issues/9000
Context: ac3b405759dfcb3f24a551e8f408ed551b78612f
In Issue #9000, we learned that:
- Constant values can change between Android API levels
-`api-merge` does not update constant values in the final `api.xml`
if they do change
Update `api-merge` to update constant values if they change, and update
`api-VanillaIceCream.xml` with the new `api-merge` logic.

[jonpryor]

@jpobstwrote:

With this updated api-VanillaIceCream.xml, the only reported constant mismatch is the one reported in #9000, which was caused by an error in our enumification process:

Mismatch: android/app/ApplicationExitInfo.REASON_OTHER 10 != 13 [API-30]

Where does this "Mismatch" message come from? I don't see anything in this PR which would emit such a message, and git grep 'Mismatch: ' doesn't find anything either.

[jpobst]

It is a quick local script I wrote that compares map.csv to api.xml.

We can leave the bones of it here for future reference:

classMismatchedEnumValues{staticstringenum_csv=@"C:\code\xamarin-android\src\Mono.Android\map.csv";staticstringapi_xml=@"C:\code\xamarin-android-backport\src\Mono.Android\Profiles\api-VanillaIceCream.xml";publicstaticvoidDo(){varconsts=ConstantsParser.FromEnumMapCsv(enum_csv).Where(c =>c.Action.In(ConstantAction.Enumify)).ToList();varxml=newXmlDocument();xml.Load(api_xml);foreach(varcinconsts){varpackage=c.JavaPackage.StartsWith("I:")?c.JavaPackage.Substring(2):c.JavaPackage;varelem=xml.SelectSingleNode($"/api/package[@name='{package.Replace('/','.')}']/*[@name='{c.JavaType.Replace('$','.')}']/field[@name='{c.JavaName}']");if(elemisnull){Console.WriteLine($"Orphan: Could not find {c.JavaPackage}.{c.JavaType}.{c.JavaName} [API-{c.ApiLevel}]");continue;}varvalue=elem.Attributes?["value"]?.Value??"";if(value!=c.Value)Console.WriteLine($"Mismatch: {c.JavaPackage}/{c.JavaType}.{c.JavaName}{c.Value} != {value} [API-{c.ApiLevel}]");}}}

(Requires a reference to Java.Interop.Tools.Generator project.)