[grouping] Allow multiple matchers of same type in fingerprinting rules

This is split off from https://github.com/getsentry/sentry/issues/84502, which has become a bit of a tangle of multiple issues.

From the relevant comment there:

> In cases where we're grouping on exception type, we don't have any way to say "give the chain with errors `A` and `B` this fingerprint", such that you could then differentiate that chain from the chain with errors `A` and `C` or the chain with errors `D` and `B`. (I tried making a rule with two `error.type` matchers, but we consider the error types in the event individually, and neither one matches both of the two-type rule's types.) This would apply to other matchers, too - you can't have multiple matchers of the same variety within a single rule. To make that work, we'd either have to change our overall logic or special-case when we see two matchers with the same key.

Start by reading issue 84502 and the fingerprinting-rule matching logic described in this issue. Determine how rules with repeated matchers are evaluated, then verify that chains containing A+B, A+C, and D+B can receive distinct fingerprints without breaking existing matcher behavior.

Written by the indexing model from the issue text.