Rename WIN64EXCEPTIONS to FEATURE_EH_FUNCLETS. (dotnet/coreclr#26220)

Rename WIN64EXCEPTIONS to FEATURE_EH_FUNCLETS. (dotnet/coreclr#26220)

* Use FEATURE_EH_FUNCLETS in jit as WIN64EXCEPTIONS is used in VM.

It will help as to add this as global defenition and replace WIN64EXCEPTIONS with it.

* Make FEATURE_EH_FUNCLETS available for VM.

Note that we do not add this define to jit\linuxnonjit for x86,
because it needs FEATURE_PAL to be defined on x86 Linux and
FEATURE_PAL is not defined when we are running linux altjit on Windows.

* Rename WIN64EXCEPTIONS to FEATURE_EH_FUNCLETS.

* Delete WIN64EXCEPTIONS.

That was confusing because it was defined on Linux x64/arm64 and on Windows arm32.

* Define DFEATURE_EH_FUNCLETS later in the file, with a condition.

* Fix two typos in comments.

Commit migrated from https://github.com/dotnet/coreclr/commit/84d4ed44b5c7f1b3db6e9ae3c71e8e1bb585bbaf