Implement -edition=YYYY semantics

[ntrel]

Set Module.edition in constructor.
Make -edition=YYYYfilename an error as it does nothing (and also wrongly sets params.edition).
Allow a larger -edition value to override a module declaration's edition. (I think this is more useful than erroring). Note: this case is not mentioned in the DIP AFAICT - @atilaneves?

Fixes #22245.

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[rikkimax]

Yes it can lower it.

The edition switch is only for overriding the default edition (D2/legacy).

[rikkimax]

This DIP also recommends a -E switch that allows the user to specify a default target edition for all imported modules in a given path. This target overrides the default edition and the -edition flag, if present, for modules in the given path. An example:

The purpose of the switch is for build managers like dub.

[rikkimax]

I'll repeat myself on the issue.

The behaviour of the edition switch was purposefully decided not to override the module declaration; as-is, this PR cannot be accepted.

[ntrel]

The behaviour of the edition switch was purposefully decided not to override the module declaration

OK, fixed.