[dart2wasm] Produce wrapper functions for closures

Instead of using top types for the parameters and return of the
implementation function for a function expression or local function,
use precise types and generate a wrapper function with top types that
casts the parameters and calls the implementation function.

This unifies the wrapper function generation with tear-offs, setting
the stage for the upcoming generalization to support type parameters
and optional parameters.

The change also brings some benefits in its own right:
- Arguments to closures are converted once instead of at every use
- Direct calls to local functions avoid the conversion of arguments

Also add source location to closure function names and generally avoid
parentheses in function names, as they are confusing in stack traces.

Change-Id: If83073bb2e2dd17554ffa03fa2596e79d730fb67
Cq-Include-Trybots: luci.dart.try:dart2wasm-linux-x64-d8-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/256665
Reviewed-by: Joshua Litt <joshualitt@google.com>