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.

Fixes #1349.

Regression from ce676cf1.

We need to output (*d).mx rather than *d.mx, at least according to Tint.
wgsl-in seems to handle *d.mx just fine, which is likely a separate bug.

* Make span copyable

* Use fixed size integers for span

* [spv-in] New two pass parser based

* [spv-in] Allow expressions defined in dominant block in different scopes

* Make the patch non breaking

* [spv-in] Allow scope transfers in phi instructions

* [spv-in] Remove unused stuff

* [spv-in] Handle switch merges as breaks

* Remove no longer needed stuff

* Revert some changes to prepare to merge

* Remove dead code

* Don't spill into local if in scope

* [spv-in] Documentation, comments, some renaming for clarity.

* Address comments

Co-authored-by: Jim Blandy <jimb@red-bean.com>

Fixes #1322.