Fix attribute exclusion

[bddckr]

Closes #883

The following changes have been added additionally:

• Reduce allocations to be done once only.
• Update the documentation to get rid of a mistake: Fully qualified attribute type names are actually not supported. I checked all the other documentation documents - they are already OK.

[dnfadmin]

All CLA requirements met.

[MarcoRossignoli]

Thanks, can you add a test with attribute doesn't end with Attribute?
You can add a test near https://github.com/coverlet-coverage/coverlet/blob/master/test/coverlet.core.tests/Instrumentation/InstrumenterTests.cs#L125 and a sample near https://github.com/coverlet-coverage/coverlet/blob/master/test/coverlet.core.tests/Samples/Samples.cs#L205

[bddckr]

@MarcoRossignoli I totally forgot about those 😅 Added now. Let me know if you think the test changes are OK. I figured there's no need to create a custom attribute type as the one that originally gave us issues can be referenced directly in the tests. I also didn't add any specific test for this and instead updated the various exclusion tests so they all test this case, too.

[bddckr]

I had to update the CecilSymbolHelperTests to make the tests pass. I think that is needed due to me adding a test class into DeclaredConstructorClass, but let me know if that is wrong.

[MarcoRossignoli]

Thanks I'll take a look asap

[MarcoRossignoli]

I had to update the CecilSymbolHelperTests to make the tests pass. I think that is needed due to me adding a test class into DeclaredConstructorClass, but let me know if that is wrong.

It's ok, it's related to new using on top of sample file, moved all lines below

[MarcoRossignoli]

LGTM thans's!