docs: Add highlighting for devicetree and kconfig

Added syntax highlighting for devicetree and kconfig files.

The PrismJS project is not accepting contributions right now as they
work on a version 2 of the library, so the new language files are added
directly here.

Also enabled syntax highlighting for various languages that are used in
the docs but aren't enabled in Docusaurus by default.

docs/src/theme/prism/components/prism-kconfig.js

@@ -0,0 +1,44 @@
+/**
+ * Copyright (c) 2023 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+/* eslint-disable no-undef */
+
+Prism.languages.kconfig = {
+  comment: {
+    pattern: /(^|[^\\])#.*/,
+    lookbehind: true,
+    greedy: true,
+  },
+  string: /"(?:\\.|[^\\\r\n"])*"/,
+  helptext: {
+    // help text ends at the first line at a lower level of indentation than the
+    // first line of text.
+    pattern: /(^\s*)(?:help|---help---)\s*^(\s+)(?:.+)(?:\s*^\2[^\n]*)*/m,
+    lookbehind: true,
+    alias: "string",
+    inside: {
+      keyword: /^(?:help|---help---)/,
+    },
+  },
+  keyword:
+    /\b(?:allnoconfig_y|bool|boolean|choice|comment|config|def_bool|def_hex|def_int|def_string|def_tristate|default|defconfig_list|depends|endchoice|endif|endmenu|env|hex|if|imply|int|mainmenu|menu|menuconfig|modules|on|option|optional|orsource|osource|prompt|range|rsource|select|source|string|tristate|visible)\b/,
+  expansion: {
+    pattern: /\$\([\s\S]+\)/,
+    alias: "variable",
+    inside: {
+      function: /\$\(|\)/,
+      punctuation: /,/,
+    },
+  },
+  number: /\b(?:0[xX][0-9a-fA-F]+|\d+)/,
+  boolean: {
+    pattern: /\b(?:y|n|m)\b/,
+    alias: "number",
+  },
+  variable: /\b[A-Z_]+\b/,
+  operator: /[<>]=?|[!=]=?|&&|\|\|/,
+  punctuation: /[()]/,
+};