Emit and report missing `Decimal-` and `DateTimeConstantAttribute`

[jjonescz]

Fixes #65728.

• Emits those attributes for synthesized delegates and closure implementation methods.
• Reports if those attribute types are missing (instead of crashing on Debug.Assert during emit) for synthesized delegates, methods, local functions, lambdas, and fields.

Relates to lambda default parameters.

[AlekseyTs]

Done with review pass (commit 2)

[AlekseyTs]

Done with review pass (commit 14)

[AlekseyTs]

            // check that the corresponding `*ConstantAttribute` is available.

It is not clear to me why this check was relevant here and isn't relevant any more. It feels to me that checking for System_ParamArrayAttribute__ctor and for these attributes should always come together.

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In reply to: 1353581343

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In reply to: 1353581343

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Refers to: src/Compilers/CSharp/Portable/Binder/Semantics/Conversions/Conversions.cs:72 in ebf1101. [](commit_id = ebf11012711cc15756843eb014d271b6ba52b971, deletion_comment = True)

[AlekseyTs]

Done with review pass (commit 40)

[AlekseyTs]

Done with review pass (commit 46)

[AlekseyTs]

            if (isSynthesized && defaultValue != ConstantValue.NotAvailable &&

Dropped the != ConstantValue.NotAvailable check. Doesn't look intentional. #Closed

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Refers to: src/Compilers/CSharp/Portable/Binder/Binder_Conversions.cs:793 in 589ff29. [](commit_id = 589ff29cd98b87c45a20c28eb312477125886c02, deletion_comment = True)

[AlekseyTs]

            if (isSynthesized && defaultValue != ConstantValue.NotAvailable &&

I see, that was equivalent to the null check

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In reply to: 1358063599

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Refers to: src/Compilers/CSharp/Portable/Binder/Binder_Conversions.cs:793 in 589ff29. [](commit_id = 589ff29cd98b87c45a20c28eb312477125886c02, deletion_comment = True)

[jjonescz]

@dotnet/roslyn-compiler for the second review