Improve text for OpenSsl primitives when OpenSSL is not available

[vcsjones]

When using any of the *OpenSsl primitives on macOS, the current exception text is somewhat confusing. Before, it would be

Algorithm 'ECDiffieHellmanOpenSsl' is not supported on this platform.

After this change, it will be:

Algorithm 'ECDiffieHellmanOpenSsl' requires OpenSSL however OpenSSL could not be found or loaded.

This only affects using the *OpenSsl primitives on macOS since it is the only platform where we "support" OpenSSL but don't outright require it. Windows, Android etc. will continue to use the OpenSsl.NotSupported.cs in their complication targets:

runtime/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/OpenSsl.NotSupported.cs

Lines 74 to 77 in ae4d698

	public ECDiffieHellmanOpenSsl()
	{
	throw new PlatformNotSupportedException(SR.PlatformNotSupported_CryptographyOpenSSL);
	}

So those platforms will continue to receive the former exception message.

cc @mvoss84

Contributes to #89006

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Issue Details

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When using any of the *OpenSsl primitives on macOS, the current exception text is somewhat confusing. Before, it would be

Algorithm 'ECDiffieHellmanOpenSsl' is not supported on this platform.

After this change, it will be:

Algorithm 'ECDiffieHellmanOpenSsl' requires OpenSSL however OpenSSL could not be found or loaded.

This only affects using the *OpenSsl primitives on macOS since it is the only platform where we "support" OpenSSL but don't outright require it. Windows, Android etc. will continue to use the OpenSsl.NotSupported.cs in their complication targets:

runtime/src/libraries/System.Security.Cryptography/src/System/Security/Cryptography/OpenSsl.NotSupported.cs

Lines 74 to 77 in ae4d698

	public ECDiffieHellmanOpenSsl()
	{
	throw new PlatformNotSupportedException(SR.PlatformNotSupported_CryptographyOpenSSL);
	}

So those platforms will continue to receive the former exception message.

cc @mvoss84

Contributes to #89006

Author:	vcsjones
Assignees:	vcsjones
Labels:	area-System.Security
Milestone:	-