Refactor sidebar assignee&milestone&project selectors (#32465)

Follow #32460

Now the code could be much clearer than before and easier to maintain. A
lot of legacy code is removed.

Manually tested.

This PR is large enough, that fine tunes could be deferred to the future if
there is no bug found or design problem.

Screenshots:

<details>

![image](https://github.com/user-attachments/assets/35f4ab7b-1bc0-4bad-a73c-a4569328303c)

</details>

modules/base/tool.go

@@ -147,6 +147,9 @@ func StringsToInt64s(strs []string) ([]int64, error) {
 	}
 	ints := make([]int64, 0, len(strs))
 	for _, s := range strs {
+		if s == "" {
+			continue
+		}
 		n, err := strconv.ParseInt(s, 10, 64)
 		if err != nil {
 			return nil, err

modules/base/tool_test.go

@@ -152,6 +152,7 @@ func TestStringsToInt64s(t *testing.T) {
 	}
 	testSuccess(nil, nil)
 	testSuccess([]string{}, []int64{})
+	testSuccess([]string{""}, []int64{})
 	testSuccess([]string{"-1234"}, []int64{-1234})
 	testSuccess([]string{"1", "4", "16", "64", "256"}, []int64{1, 4, 16, 64, 256})
 

modules/container/set.go

@@ -31,8 +31,8 @@ func (s Set[T]) AddMultiple(values ...T) {
 	}
 }
 
-// Contains determines whether a set contains the specified elements.
-// Returns true if the set contains the specified element; otherwise, false.
+// Contains determines whether a set contains all these elements.
+// Returns true if the set contains all these elements; otherwise, false.
 func (s Set[T]) Contains(values ...T) bool {
 	ret := true
 	for _, value := range values {

modules/container/set_test.go

@@ -18,7 +18,9 @@ func TestSet(t *testing.T) {
 
 	assert.True(t, s.Contains("key1"))
 	assert.True(t, s.Contains("key2"))
+	assert.True(t, s.Contains("key1", "key2"))
 	assert.False(t, s.Contains("key3"))
+	assert.False(t, s.Contains("key1", "key3"))
 
 	assert.True(t, s.Remove("key2"))
 	assert.False(t, s.Contains("key2"))

modules/templates/helper.go

@@ -31,6 +31,7 @@ func NewFuncMap() template.FuncMap {
 		"ctx": func() any { return nil }, // template context function
 
 		"DumpVar": dumpVar,
+		"NIL":     func() any { return nil },
 
 		// -----------------------------------------------------------------
 		// html/template related functions