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).

modules/util/io.go

@@ -9,7 +9,7 @@ import (
 )
 
 // ReadAtMost reads at most len(buf) bytes from r into buf.
-// It returns the number of bytes copied. n is only less then len(buf) if r provides fewer bytes.
+// It returns the number of bytes copied. n is only less than len(buf) if r provides fewer bytes.
 // If EOF occurs while reading, err will be nil.
 func ReadAtMost(r io.Reader, buf []byte) (n int, err error) {
 	n, err = io.ReadFull(r, buf)