Simplify patch handling

[agateau-gg]

Context

While reviewing #905 I thought it was a bit sad that we had to add a field just for backward-compatibility, so I dived into what could be done to get rid of some of the patch special-cases cruft.

What has been done

Line.content now always contains the full line, including the patch symbol.

This simplifies a bunch of things:

• MatchSpan.from_match() no longer cares about is_patch
• ExtendedMatch.from_match() can reuse match.match as is
• SecretTextOutputHandler no longer needs to reprint the patch symbol
• Line.category is gone, it's replaced by a is_patch boolean. This attribute is only used to decide whether to print patch or file line numbers.

If you look at the snapshot diff you will see two things.

First, patch output is more correct: the second @ at the end of the @@ ... @@ lines does not miss anymore.

For multiline secrets, the detector left "arm" (the |___ symbol) starts one character earlier (see the snapshot diffs). This might be fixable but I don't think it's a problem.

Validation

Tests still pass.

PR check list

• [x] As much as possible, the changes include tests (unit and/or functional)
• [x] If the changes affect the end user (new feature, behavior change, bug fix) then the PR has a changelog entry (see doc/dev/getting-started.md). If the changes do not affect the end user, then the skip-changelog label has been added to the PR.

[agateau-gg]

You set this PR to your original fix branch, instead of garancegourdel/refacto-output-handlers-to-remove-scanable-from-result is that intentional ?

Oups, I missed that the branch had been created. Going to rebase.

You have functional test failing because they capture a new generic secret in the snapshot.

Should be good now 🤞🏻.