Add rule suggesting use of const instead of global

rule-tests/__snapshots__/use-const-snapshot.yml

@@ -0,0 +1,40 @@
+id: use-const
+snapshots:
+  global a = b"";:
+    fixed: const a = b"";
+    labels:
+    - source: global
+      style: primary
+      start: 0
+      end: 6
+    - source: b""
+      style: secondary
+      start: 11
+      end: 14
+    - source: b""
+      style: secondary
+      start: 11
+      end: 14
+    - source: global a = b"";
+      style: secondary
+      start: 0
+      end: 15
+  global x = 1;:
+    fixed: const x = 1;
+    labels:
+    - source: global
+      style: primary
+      start: 0
+      end: 6
+    - source: '1'
+      style: secondary
+      start: 11
+      end: 12
+    - source: '1'
+      style: secondary
+      start: 11
+      end: 12
+    - source: global x = 1;
+      style: secondary
+      start: 0
+      end: 13

rule-tests/use-const.yml

@@ -0,0 +1,8 @@
+id: use-const
+valid:
+  - "global x: m::X;"
+  - "global x: m::X = [];"
+  - "const x = 1;"
+invalid:
+  - "global x = 1;"
+  - 'global a = b"";'

rules/use-const.yml

@@ -0,0 +1,19 @@
+id: use-const
+message: Prefer 'const' over 'global' if possible
+severity: hint
+language: spicy
+rule:
+  kind: "linkage"
+  regex: "global"
+  inside:
+    kind: "var_decl"
+    has:
+      field: "init"
+      kind: "expression"
+      any:
+        - has:
+            kind: "bytes"
+        - has:
+            kind: "integer"
+
+fix: "const"