refactor(parse): separate self parameter parsing from general parameter parsing

[xonx4l]

Fixes #144206

The changes-:
Moves self parameter parsing out of parse_param_general and into parse_fn_params
for better separation of concerns. This removes the first_param boolean and its
branching logic while maintaining identical behavior.

Benefits:

• Cleaner separation of concerns
• Improved readability and testability
• More maintainable code structure

No behavioral changes introduced.

[rustbot]

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[nnethercote]

s/reamining_params/remaining_params/

[nnethercote]

Please fix the errors, thanks!

@rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.

[fmease]

(please also squash into one commit afterwards, thanks)

[xonx4l]

@rustbot ready

[nnethercote]

Still more CI failures to be fixed.

@rustbot author

[bors]

☔ The latest upstream changes (presumably #145423) made this pull request unmergeable. Please resolve the merge conflicts.

[nnethercote]

Sorry, I don't think this is a valid change. With the current code, the self param will be parsed within the self.collect_tokens() call in parse_param_general. This PR moves self parsing outside of the self.collect_tokens(), which means tokens will never be collected for it.

I understand your desire to clean this code up -- the first_param argument is clumsy. But I think it is necessary.