Replace `Module::apply_common_default_interpolation` with a simpler function
that handles a single `Binding` at a time. In exchange for the simplicity, the
function must be called at each point function arguments, function results, and
struct members are prepared. (Any missed spots will be caught by the verifier.)

This approach no longer requires mutating types in the arena, a prerequisite for
properly handling type identity.

Applying defaults to struct members when the struct declaration is parsed does
have a disadvantage, compared to the old whole-module pass: at struct parse
time, we don't yet know which pipeline stages the struct will be used in. The
best we can do is apply defaults to anything with a `Location` binding. This
causes needless qualifiers to appear in some output. However, it seems that our
back end languages all tolerate such qualifiers.

Previously the typifier flagged all relational functions as producing a
scalar boolean but with the exception of `all` and `any`, according to
the wgsl spec, all other relational functions output a type the same
size as the input.

Adds checks that it isn't used in an unsupported function and emits the
depth_ref as a separate argument.

Add support for float, vector and matrices targets.

Fix prefix and postfix being inverted (one was returning the value
of the other).

Remove an unneeded local indirection for prefix handling.

Add tests.

This caused arrayed textures to not be accepted

Constants that are to be dynamically indexed now are first transformed
into locals with them as the initializer.

Fixes #1352.

Without this change, the `to_range` method method returns `None` even when spans
are enabled.

Fixes #1356.

Output for the test case in that issue is now:

    error: the value indexed by a `[]` subscripting expression must not be a pointer
      ┌─ wgsl:5:14
      │
    5 │     let a = *pv[3]; // Problematic line
      │              ^^ expression is a pointer

    Could not parse WGSL

Both a `var` binding and a `let` binding of a pointer to a variable create
entries in the `lookup_ident` tables whose expression is a `LocalVariable`.
However, the `let` should be a pointer, whereas the `var` should be a reference.
This patch changes the tables to hold `TypedExpression` values, thus preserving
the distinction.

This allows removing many arguments from functions dealing with
instruction parsing

The old filenames were probably based on the shader stage, not the shader
function name, which the PR changed to do in response to a review suggestion.

`tests/out/glsl/operators.main.Fragment.glsl` is no longer generated because the
function in question changed to a Compute entry point.

`tests/out/wgsl/multiple_entry_points-glsl.wgsl` is no longer generated because
the input test was removed in 057dc310.

Make the parser code more closely follow the spec's grammar around
`unary_expression`, `postfix_expression`, and `singular_expression`.

Change the handling of postfix expressions (indexing, member/component access,
and swizzling) to apply the indirection at the appropriate time, resulting in
code improvements on all output formats. For example, where we used to generate
the following MSL:

    metal::float4 _e13 = bar.matrix[3];
    float b = _e13.x;

we now generate, simply:

    float b = bar.matrix[3].x;

Propagate WGSL reference types correctly, so that parenthesizing expressions no
longer causes the Load Rule to be applied.

Together with #1332 (already landed), this is a replacement for #1312, and
unblocks #1352.

Fixes #1351.