Closes #56445.

When the character next to `{}` is "shifted" (when mapping a byte index
in the format string to span) we should avoid shifting the span end
index, so first map the index of `}` to span, then bump the span,
instead of first mapping the next byte index to a span (which causes
bumping the end span too much).

Regression test added.

Fixes #83344

Fixes #83046

The program

    fn main() {
        println!("{:?}", '"');
        println!("{:?}", "'");
    }

would previously print

    '\"'
    "\'"

With this patch it now prints:

    '"'
    "'"

Fixes #83469

We need to return an `Annotatable::Stmt` if we were passed an
`Annotatable::Stmt`

This reverts commit 22ae20733515d710c1134600bc1e29cdd76f6b9b.

Fixes #80691

When we evaluate a trait predicate, we convert an
`EvaluatedToOk` result to `EvaluatedToOkModuloRegions` if we erased any
regions. We cache the result under a region-erased 'freshened'
predicate, so `EvaluatedToOk` may not be correct for other predicates
that have the same cache key.

Caused by
https://github.com/rust-lang/rust/commit/b0659f9b1bfb92626c40dabceb3268f88bb26224#diff-ede26372490522288745c5b3df2b6b2a1cc913dcd09b29af3a49935afe00c7e6L464-R464

Closes #80664

A bunch of nits fixed, and a new test for pretty printing the AST.

This currently creates a field which is always false on GenericParamDefKind for future use when
consts are permitted to have defaults

Update const_generics:default locations

Previously just ignored them, now actually do something about them.

Fix using type check instead of value

Add parsing

This adds all the necessary changes to lower const-generics defaults from parsing.

Change P<Expr> to AnonConst

This matches the arguments passed to instantiations of const generics, and makes it specific to
just anonymous constants.

Attempt to fix lowering bugs

This commit removes the previous mechanism of differentiating
between "Debug" and "Display" formattings for the sign of -0 so as
to comply with the IEEE 754 standard's requirements on external
character sequences preserving various attributes of a floating
point representation.

In addition, numerous tests are fixed.

In the analysis use `resolve_vars_if_possible` instead of `fully_resolve`,
because we might not have performed regionck yet.

Fixes: #83176

These tests were added to master after I made my changes.

* It is called `source` in rustc and the rest of rustdoc
* It is not a span, rather it is the source of the import

This saves us both the Freeze/Unpin queries, and avoids placing
noalias attributes, which have a compile-time impact on LLVM
even in optnone builds (due to always_inline functions).

We don't have any known noalias bugs for LLVM 12 ... yet.