Allow drivers to supply a list of extra symbols to intern

[Alexendoo]

Allows adding new symbols as consts in external drivers, desirable in Clippy so we can use them in patterns to replace code like

rust/src/tools/clippy/clippy_lints/src/casts/cast_ptr_alignment.rs

Line 66 in 75530e9

if matches!(name.ident.as_str(), "read_unaligned" | "write_unaligned")

The Clippy change adds a couple symbols as a demo, the exact clippy_utils API and replacing other usages can be done on the Clippy side to minimise sync conflicts

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[rustbot]

Some changes occurred in src/tools/clippy

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[blyxyas]

This will help a lot when having symbols on Clippy. We usually just batched these and submitted a PR to add 3 or 4 symbols at a time.

Strong +1 ! 👀

[bors]

☔ The latest upstream changes (presumably #137930) made this pull request unmergeable. Please resolve the merge conflicts.

[fee1-dead]

I would recommend keeping fresh() but naming a new method for this. Perhaps new_with_extra_preinterned_symbols?

[Alexendoo]

Renamed it to with_extra_symbols and added some docs

There's only one callsite so the current fresh would be unused

[fee1-dead]

This needs a better name and we should document what it really means. Perhaps something like

Suggested change

	pub const PREINTERNED_SYMBOLS_COUNT: u32 = #preinterned_symbols_count;
	/// The number of predefined symbols; this is the the first index for
	/// extra pre-interned symbols in an Interner created via
	/// `new_with_extra_preinterned_symbols`.
	pub const PREDEFINED_SYMBOLS_COUNT: u32 = #predefined_symbols_count;