feat: add mut LabelSpan.set_span_offset

[Sysix]

For partial linter source text, we need to modify the offset of the span.

ATM this is how the oxlint does it:
https://github.com/oxc-project/oxc/blob/f9cbe844f207c0f578285204e6ecb8d650974165/crates/oxc_diagnostics/src/service.rs#L118-L168

In this function, it converts the function to a generic Error miette object. This is not wanted for the langauge server and the tester.

The language server does it when creating the MessageWithPosition:
https://github.com/oxc-project/oxc/blob/f9cbe844f207c0f578285204e6ecb8d650974165/crates/oxc_linter/src/service/runtime.rs#L645-L676

Currently, the tester does not fix the offset for partial source texts:
oxc-project/oxc#12545 (comment)

---

The goal:

Create a Message impl: https://github.com/oxc-project/oxc/blob/f9cbe844f207c0f578285204e6ecb8d650974165/crates/oxc_linter/src/fixer/mod.rs#L276-L294

So the offset adjustment can be done in one simple place and shared for all 3 inputs.

POC: https://github.com/oxc-project/oxc/pull/12594/files

    pub fn with_offset(&mut self, offset: u32) -> &mut Self {
        if offset == 0 {
            return self;
        }

        self.span =
            Span::new(self.span.start.saturating_add(offset), self.span.end.saturating_add(offset));

        if let Some(labels) = &mut self.error.labels {
            for label in labels {
                label.set_span_offset(label.offset().saturating_add(offset as usize));
            }
        }

        self
    }

[Sysix]

• feat: add mut LabelSpan.set_span_offset #62 👈 (View in Graphite)
• main

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