This commit deprecates "import assertions" proposal that has been
replaced with "import attributes".
Any time an import assertion is encountered a warning will be printed
to the terminal. This warning will be printed for both local and
remote files (ie. user code and dependencies).
Import assertions support will be removed in Deno 2.
This change aims to replace all relative import specifiers targeted at
`tests/util/std` with mapped ones (using a `deno.json` file). Towards
updating the `std` git submodule.
I'm unsure whether we're planning to make the `Deno.FsFile` constructor
illegal or remove `FsFile` from the `Deno.*` namspace in Deno 2. Either
way, this PR works towards the former. I'll create a superceding PR if
the latter is planned instead.
Towards #23089
This change removes deprecated methods from the `Deno.*` namespace when
the `DENO_FUTURE=1` environment variable is used.
Note: this does not address deprecated class properties and methods.
E.g. `Deno.Conn.rid`.
