Add typing.Final and simplify type inference

[EmilyBourne]

Add support for typing.Final. Fixes #1680 . This means that the AST can describe everything that textx parses in type string annotations. Therefore the type annotation methods are simplified and unified to reduce code duplication. Fixes #1581. This should make it simpler to add support for tuple/list/set type annotations

Commit Summary

• Fix pickling of Variable and AnnotatedPyccelSymbol (lambda expressions can't be pickled) by moving ast.core.apply->ast.core.apply_pickle
• Remove unused redundant class UnionType
• Simplify SyntacticTypeAnnotation to only handle one type (instead of all textx output).
• Add support for typing.Final (represents is_const concept)
• Remove python_builtin_datatypes and simply use _visit_PyccelSymbol to collect type.
  It is not useful to differentiate between datatypes and functions. The two dictionaries point at the same objects and Python itself doesn't differentiate between the two. Anything that was missing was moved into buitin_functions.
• Fix unnecessary import of deprecated types from NumPy in generated Python code.
• Stop duplicating textx logic.
• Add _get_indexed_type function to handle IndexedElement objects which describe a type.
• Use textx class descriptors to generate Pyccel AST elements that can be parsed in the semantic stage.
• Fix bug in test where floats were passed instead of NumPy floats.
• Stop raising a warning when the order is provided unnecessarily.
• Fix minor bot bug when whole file is new code.
• Add is_const setter to type annotations.
• Fix pyccel-init script which was not calling the related function.

[pyccel-bot]

Hello again! Thank you for this new pull request 🤩.

Please begin by requesting your checklist using the command /bot checklist

[Farouk-Echaref]

Features I haven't used yet have helped me gain more insights for the project.

[pyccel-bot]

Hey @yguclu, @EmilyBourne, this PR is looking pretty good. @EmilyBourne and @Farouk-Echaref think it is ready to merge. Could you add your expertise to confirm that this follows all the coding conventions and fits in Pyccel's future plans? Thanks 😄

[yguclu]

/bot run pr_tests

[pyccel-bot]

There seems to be lines in this PR which aren't tested. Please take a look at my comments and add tests which cover the new code.

If this is modified code which cannot be easily tested in this PR please open an issue to request that this code be either removed or tested. Once you have done that please leave a message on the relevant conversation beginning with the line /bot accept and referencing the issue.

Similarly if the new code cannot be tested for some reason, please leave a comment beginning with the line /bot accept on the relevant conversation explaining why the code can't be tested.

[pyccel-bot]

This code isn't tested. Please can you take a look

[EmilyBourne]

/bot accept

This doesn't really make sense at the moment but it is necessary to describe everything that is possible according to our type grammar.

[pyccel-bot]

Unfortunately your PR is not passing the tests so it is not quite ready for review yet. Let me know when it is fixed with /bot mark as ready.

[pyccel-bot]

Good job ! Your PR is using all the code it added/changed.