Use TypingMode throughout the compiler instead of ParamEnv

[lcnr]

Hopefully the biggest single PR as part of rust-lang/types-team#128.

infcx.typing_env while defining opaque types

I don't know how'll be able to correctly handle opaque types when using something taking a TypingEnv while defining opaque types. To correctly handle the opaques we need to be able to pass in the current opaque_type_storage and return constraints, i.e. we need to use a proper canonical query. We should migrate all the queries used during HIR typeck and borrowck where this matters to proper canonical queries. This is

layout_of and Reveal::All

We convert the ParamEnv to Reveal::All right at the start of the layout_of query, so I've changed callers of layout_of to already use a post analysis TypingEnv when encountering it.

rust/compiler/rustc_ty_utils/src/layout.rs

Line 51 in ca87b53

let param_env = param_env.with_reveal_all_normalized(tcx);

Ty::is_[unpin|sized|whatever]

I haven't migrated fn is_item_raw to use TypingEnv, will do so in a followup PR, this should significantly reduce the amount of typing_env.param_env. At some point there will probably be zero such uses as using the type system while ignoring the typing_mode is incorrect.

MirPhase and phase-transitions

When inside of a MIR-body, we can mostly use its MirPhase to figure out the right typing_mode. This does not work during phase transitions, most notably when transitioning from Analysis to Runtime:

rust/compiler/rustc_mir_transform/src/lib.rs

Lines 606 to 625 in dae7ac1

	// These next passes must be executed together.
	&add_call_guards::CriticalCallEdges,
	// Must be done before drop elaboration because we need to drop opaque types, too.
	&reveal_all::RevealAll,
	// Calling this after reveal_all ensures that we don't deal with opaque types.
	&add_subtyping_projections::Subtyper,
	&elaborate_drops::ElaborateDrops,
	// This will remove extraneous landing pads which are no longer
	// necessary as well as forcing any call in a non-unwinding
	// function calling a possibly-unwinding function to abort the process.
	&abort_unwinding_calls::AbortUnwindingCalls,
	// AddMovesForPackedDrops needs to run after drop
	// elaboration.
	&add_moves_for_packed_drops::AddMovesForPackedDrops,
	// `AddRetag` needs to run after `ElaborateDrops` but before `ElaborateBoxDerefs`.
	// Otherwise it should run fairly late, but before optimizations begin.
	&add_retag::AddRetag,
	&elaborate_box_derefs::ElaborateBoxDerefs,
	&coroutine::StateTransform,
	&Lint(known_panics_lint::KnownPanicsLint),

All these passes still run with MirPhase::Analysis, but we should only use Reveal::All once we're run the RevealAll pass. This required me to manually construct the right TypingEnv in all these passes. Given that it feels somewhat easy to accidentally miss this going forward, I would maybe like to change Body::phase to an Option and replace it at the start of phase transitions. This then makes it clear that the MIR is currently in a weird state.

r? @ghost