Officially support TypeScript 5

[ejizba]

TypeScript v5 was released in March 2023. It's possible customers already got our package working with TS v5, but we need to investigate and officially add support.

Ideally we can support TypeScript v4 and v5 at the same time, but if not we should switch to TS v5 when we do the next major version of the @azure/functions package.

We have unit tests to cover TypeScript versions, which would need some updating:

• Add TS v5 in package.json similar to how we have "typescript4": "typescript5": "npm:typescript@~5.0.0"
  • NOTE: There's a difference between the TS version used to build our code (the default) and these ones which are only used for testing. The test versions should be on minimum supported major versions for ideal validation, which is why they use "~" instead of "^"
• Add '5' to the array of versions in the test here
• Add several default functions to this file. You can compare to the v3.x branch to see what it should look like. Apparently we removed this temporarily for the new model and never added it back