Previously, AK::Function would accept _any_ callable type, and try to
call it when called, first with the given set of arguments, then with
zero arguments, and if all of those failed, it would simply not call the
function and **return a value-constructed Out type**.
This lead to many, many, many hard to debug situations when someone
forgot a `const` in their lambda argument types, and many cases of
people taking zero arguments in their lambdas to ignore them.
This commit reworks the Function interface to not include any such
surprising behaviour, if your function instance is not callable with
the declared argument set of the Function, it can simply not be
assigned to that Function instance, end of story.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
This commit makes the user-facing StdLibExtras templates and utilities
arguably more nice-looking by removing the need to reach into the
wrapper structs generated by them to get the value/type needed.
The C++ standard library had to invent `_v` and `_t` variants (likely
because of backwards compat), but we don't need to cater to any codebase
except our own, so might as well have good things for free. :^)
