Highlight capturing lambdas

[alrz]

Even with static lambdas, it's hard to spot capturing lambdas that are not intended to be.

A different formatting such as underlining => would help to fix those and possibly mark as static.

[sharwell]

There are 4 scenarios where I've needed information related to this:

1. The lambda captures one or more arguments to the method and the method contains a path to return which does not construct the lambda. In this case, the arguments will be placed in a box (with allocation) even when the lambda delegate is not created.
2. The lambda does not capture anything (effectively static).
3. The lambda only captures this (non-static).
4. The lambda captures one or more locals/arguments, and thus will always trigger an allocation for the creation of the delegate.

[Cosifne]

Design meeting conclusion:
We want to solve the problem by layering, also we don’t oppose to if it is a capturing lambda behind, underlying the arrow operator. But we prefer the layer way.)

[alrz]

There are 4 scenarios where I've needed information related to this:

That seems to overlap with a general feature to highlight allocations. Is that something to consider here?

edit: It's already here: https://github.com/microsoft/RoslynClrHeapAllocationAnalyzer