Add the ability to ignore suppressions in SuppressibleTreePathScanner

[kelvinou01]

Before this PR

We are working on -PerrorProneRemoveUnused, a mode which removes all unused suppressions. This mode requires us to turn on the ignore suppressions option in error-prone, or else we can't descend into suppressed trees to chec.

Error-prone's SuppressibleTreePathScanner doesn't respect this flag. This is not expected behavior, as ErrorProneScanner respects the flag. We've opened google/error-prone#5255, but I think it will take some time to be merged. In the mean time, let's add the option to insert some bytecode so the SuppressibleTreePathScanner respects this flag when we need it to.

After this PR

==COMMIT_MSG==
Add the ability to ignore suppressions in SuppressibleTreePathScanner
==COMMIT_MSG==

Possible downsides?

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Description

Add the ability to ignore suppressions in SuppressibleTreePathScanner

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✨ Features

• Add the ability to ignore suppressions in SuppressibleTreePathScanner (#200)

[CRogers]

EntryStream has a slightly shorter .toMap(mergeFunction) method.

[CRogers]

So this is letting us natively has the same option multiple times, which then builds them up as a list (aka comma separated string argument)?

[CRogers]

Why do we actually need this change?

[kelvinou01]

Oops I think this was required to handle some extra options in the next PR. Can't remember why exactly it was needed, but let's remove it from this PR.

[autorelease3]

Released 2.21.0