Highlight visibility method arguments and stop highlighting shadowing locals

[tarebyte]

Problem

Follow-up to #8. That PR moved private, protected and public off @keyword, but it only covers the bare form. Two cases on master are still wrong.

A local variable that shadows one of the names is highlighted as a method call. These names can be shadowed, which was part of #8's own argument for not treating them as keywords:

private = 1
private     # highlighted as function.method.builtin, but it is a local read

This was already wrong before #8 — it rendered as keyword — so #8 changed which wrong capture it gets rather than fixing it.

The argument forms do not get the built-in capture at all. private :foo and private def bar; end parse as a call, which the general (call method: (identifier) @function.method) pattern claims. Later patterns win, so the identifier pattern added in #8 never applies to them:

expected highlight 'function.method.builtin', actual highlights: 'function.method'

That leaves private and private :foo rendering differently from each other.

Change

• Adds #is-not? local to the identifier pattern. The query file already uses exactly this guard on the general @function.method identifier pattern a few lines above, so this follows the existing convention rather than introducing one.
• Adds a call pattern after the general call pattern, which is where the require pattern already sits for the same precedence reason. !receiver keeps an unrelated method that happens to share a name, such as acl.public, an ordinary call.

Validation

332 corpus parses and 5 highlight files, zero failures. test/highlight/classes.rb goes from 14 to 19 assertions:

Source	Capture
private (bare)	function.method.builtin
private :with_symbol	function.method.builtin
private def with_def; end	function.method.builtin
private = 1 then a bare private	variable
acl.public	function.method

Each new assertion was confirmed to fail without its pattern. Removing #is-not? local gives expected highlight 'variable', actual highlights: 'function.method.builtin'; removing the call pattern gives expected highlight 'function.method.builtin', actual highlights: 'function.method'.