Fixes #1322.

This was causing warnings in nightly (1.56.0).

* Fix GLSL output for non-fallthrough switch cases

Partially reverts 02c74b50021379092a9d4567fd11aeb0879c5405 and
fixes #1309.

* Fix indentation of control-flow WGSL code

* Clean up glsl-out switch case fallthrough handling

Only insert a break if needed
and if a case is fallthrough, insert a comment indicating this.

* Implement fuzzing for the GLSL parser

* Remove arbitrary dependency from naga

Derive `Arbitrary` for proxy objects in `fuzz/fuzz_targets/glsl_parser.rs`
instead.

* [glsl-in] Allow code after terminator statements

* [glsl-in] Track finished state in the context

* [glsl-in] Cull statements after terminators

Fixes #1305.

Ensure that two `back::spv::LocalType::Image` values are sure to be equal (and
hash equal) whenever they would generate the same `OpTypeImage` instruction, so
that the usual duplicate removal via `Writer::lookup_type` works. Accomplish
this by changing the contents of `LocalType::Image` to more closely match the
operands of `OpTypeImage` instructions.

Previously, `LocalType::Image` included a `ImageClass::Storage::access` value,
which did not affect the `OpTypeImage` instruction generated. If two
`LocalType::Image` values differered only in their `access`, then they would get
separate entries in `Writer::lookup_type`, two identical `OpTypeImage`
instructions would be generated, and SPIR-V validation would fail.

This affects a lot of snapshots, so it's in its own commit, for easier review.

Change `write_type_declaration_local` to handle any type that can be represented
as a `LocalType`. This means that Image and Sampler types are handled there now.

Change `write_type_declaration_arena` to defer to `write_type_declaration_local`
to handle any type that can be represented as a `LocalType`. This makes the code
for those types in `write_type_declaration_arena` redundant, so remove it.

However, continue to request SPIR-V capabilities for image types from
`write_type_declaration_arena`, since that function is fallible, while
`write_type_declaration_local` is not.

Fixes #1030.
Fixes #1017.

When we are leaning on robust buffer access to do the job for us, there's no
undefined behavior going on. So `UndefinedBehavior` suggests people are doing
something reckless even if they're not. The policy just says what Naga is doing,
and it shouldn't pretend to say what the rest of the system is doing.

Set naga features in `fuzz/Cargo.toml` to those required for SPIR-V and
WGSL input.
Also bump libfuzzer-sys version.