Customizability Extensions: CFunction Signatures and Code Literals

This MR extends the expressivity of CFunction by allowing users to specify its type signature, and introduces literal expressions.

• CFunction Signature: Instances of CFunction now have to be created with a fixed type signature, which is used by the typifier.
• Literal expressions: Introduce PsLiteral and PsLiteralExpr to allow injection of custom code literals into the AST. Literals must have a fixed type, and are considered constant within the scope of a kernel.

This MR furthermore fixes CFunction printing, and a bug that affected typification and constant elimination in the presence of array initializers.

• Test cases for literals

added feature label

requested review from @he66coqe

assigned to @da15siwa

changed the description

approved this merge request

Nice that you already implemented this. Now I can remove it from my TODO list :).

added 12 commits

• fafe58ec...3ee5d9b6 - 11 commits from branch backend-rework
• 9bfaa437 - Merge branch 'backend-rework' into ast_extensions

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added 1 commit

• 919ed1c7 - Add literals test. Cleaned up some other tests.

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marked this merge request as ready

added 3 commits

• 919ed1c7...e512822b - 2 commits from branch backend-rework
• fa509a86 - Merge branch 'backend-rework' into ast_extensions

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marked the checklist item Test cases for literals as completed

enabled an automatic merge when the pipeline for fa509a86 succeeds

mentioned in commit 4b2de595

merged