* 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.

* Implement lexing for all WGSL number literal types

* Move number literal test cases

* Adjust tests to match WGSL spec on number literals

Suffixes are not type names and currently only a plain `u` is supported
for uints. More specifically, `i` and `f` suffixes or suffixes with
widths in bits like `u32` are not supported at the moment.

* Add more tests for invalid number literal suffixes

* Replace code too new for Rust 1.43

* Implement parsing for hexadecimal integers

* Switch to enum number types, and Bytes for width

* Check for negative and leading zeros in int literals

* Implement parsing of hex floats with hexf-parse

* Update error message tests

* Update snapshot test output files

* Clean up lexer state machine code

* Clean up unexpected token error code

* Move number literal parsing to own submodule

Using 1D images should require either the `Sampled1D` or `Image1D` capability.

Using cube array images should require either the `SampledCubeArray` or
`ImageCubeArray` capability.

Introduce a helper type that manages the details of emitting SPIR-V
conditionals, tracking labels, branches, merge annotations and phi nodes.

Change index bounds checks to use this helper.

For ease of review, there should be no meaningful code changes in this commit.
Match arms are merely moved out into their own functions, whose arguments are
the enum variant's fields, along with any free variables from the function
containing the match.