Refactor legacy unknwon/com package, improve golangci lint (#19284)

The main purpose is to refactor the legacy `unknwon/com` package.
1. Remove most imports of `unknwon/com`, only `util/legacy.go` imports the legacy `unknwon/com`
2. Use golangci's depguard to process denied packages
3. Fix some incorrect values in golangci.yml, eg, the version should be quoted string `"1.18"`
4. Use correctly escaped content for `go-import` and `go-source` meta tags
5. Refactor `com.Expand` to our stable (and the same fast) `vars.Expand`, our `vars.Expand` can still return partially rendered content even if the template is not good (eg: key mistach).

.golangci.yml

@@ -18,6 +18,7 @@ linters:
     - ineffassign
     - revive
     - gofumpt
+    - depguard
   enable-all: false
   disable-all: true
   fast: false
@@ -65,7 +66,15 @@ linters-settings:
       - name: modifies-value-receiver
   gofumpt:
     extra-rules: true
-    lang-version: 1.18
+    lang-version: "1.18"
+  depguard:
+    # TODO: use depguard to replace import checks in gitea-vet
+    list-type: denylist
+    # Check the list against standard lib.
+    include-go-root: true
+    packages-with-error-message:
+      - encoding/json: "use gitea's modules/json instead of encoding/json"
+      - github.com/unknwon/com: "use gitea's util and replacements"
 
 issues:
   exclude-rules:
@@ -153,5 +162,6 @@ issues:
     - path: models/user/openid.go
       linters:
         - golint
-    - linters: staticcheck
+    - linters:
+        - staticcheck
       text: "strings.Title is deprecated: The rule Title uses for word boundaries does not handle Unicode punctuation properly. Use golang.org/x/text/cases instead."