feat!: align standard captures with upstream

Problem: Sharing highlight queries with upstream tree-sitter and
Helix is difficult.

Solution: Where reasonable, use capture names in tree-sitter's standard
list or Helix's Atom-style hierarchy.

Specifically:

* tree-sitter "standard capture names"
  (3f44b89685/highlight/src/lib.rs (L20-L72)):

  - `@parameter` -> `@variable.parameter`
  - `@field` -> `@variable.member`
  - `@namespace` -> `@module`
  - `@float` -> `@number.float`
  - `@symbol` -> `@string.special.symbol`
  - `@string.regex` -> `@string.regexp`
  - `@text.*` -> `@markup.*` (`strong`, `italic`, `link`, `strikethrough`; with exceptions; see below)
  - `@text.title` -> `@markup.heading`
  - `@text.literal` -> `@markup.raw`
  - `@text.reference` -> `@markup.link`
  - `@text.uri` -> `@markup.link.url` (in markup links)
  - `@string.special` -> `@markup.link.label` (non-url links)
  - `@punctuation.special` -> `@markup.list` (markdown lists only; move subitems from `@text.todo`)

* Helix captures
  (https://docs.helix-editor.com/master/themes.html#syntax-highlighting):

  - `@method` -> `@function.method`
  - `@method.call` -> `@function.method.call`
  - `@text.{todo,warning,note,danger}` -> `@comment.{error,warning,hint,info,todo}`
  - `@text.diff.{add,delete,}` -> `@diff.{plus,minus,delta}`
  - `@text.uri` -> `@string.special.url` (outside markup)
  - `@preproc` -> `@keyword.directive`
  - `@define` -> `@keyword.directive`(`.define`?)
  - `@storageclass` -> `@keyword.storage`
  - `@conditional` -> `@keyword.conditional`
  - `@debug` -> `@keyword.debug`
  - `@exception` -> `@keyword.exception`
  - `@include` -> `@keyword.import`
  - `@repeat` -> `@keyword.repeat`

* cleanup

  - remove some redundant `@conceal` (but still allow it for conceal-only patterns)
  - remove obsolete `@error` (syntax linting is out of scope for this repo)
  - sort, cleanup capture list in `CONTRIBUTING.md`

queries/racket/highlights.scm

@@ -11,7 +11,7 @@
 (number) @number
 (character) @character
 (boolean) @boolean
-(keyword) @symbol
+(keyword) @string.special.symbol
 
 ;; string ;;
 
@@ -21,7 +21,7 @@
 
 (escape_sequence) @string.escape
 
-(regex) @string.regex
+(regex) @string.regexp
 
 ;; comment ;;
 
@@ -46,7 +46,7 @@
 
 ;; quote ;;
 
-(quote) @symbol
+(quote) @string.special.symbol
 
 ;; list ;;
 
@@ -125,14 +125,14 @@
 
 (list
  .
- (symbol) @include
- (#eq? @include "require")
+ (symbol) @keyword.import
+ (#eq? @keyword.import "require")
  (#set! "priority" 101))
 
 (quote
   .
   (symbol)
-  (#set! "priority" 105)) @symbol
+  (#set! "priority" 105)) @string.special.symbol
 
 ((sexp_comment) @comment
  (#set! "priority" 110))