Improve issue & code search (#33860)

Each "indexer" should provide the "search modes" they support by
themselves. And we need to remove the "fuzzy" search for code.

modules/indexer/indexer.go

@@ -0,0 +1,54 @@
+// Copyright 2025 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package indexer
+
+type SearchModeType string
+
+const (
+	SearchModeExact  SearchModeType = "exact"
+	SearchModeWords  SearchModeType = "words"
+	SearchModeFuzzy  SearchModeType = "fuzzy"
+	SearchModeRegexp SearchModeType = "regexp"
+)
+
+type SearchMode struct {
+	ModeValue    SearchModeType
+	TooltipTrKey string
+	TitleTrKey   string
+}
+
+func SearchModesExactWords() []SearchMode {
+	return []SearchMode{
+		{
+			ModeValue:    SearchModeExact,
+			TooltipTrKey: "search.exact_tooltip",
+			TitleTrKey:   "search.exact",
+		},
+		{
+			ModeValue:    SearchModeWords,
+			TooltipTrKey: "search.words_tooltip",
+			TitleTrKey:   "search.words",
+		},
+	}
+}
+
+func SearchModesExactWordsFuzzy() []SearchMode {
+	return append(SearchModesExactWords(), []SearchMode{
+		{
+			ModeValue:    SearchModeFuzzy,
+			TooltipTrKey: "search.fuzzy_tooltip",
+			TitleTrKey:   "search.fuzzy",
+		},
+	}...)
+}
+
+func GitGrepSupportedSearchModes() []SearchMode {
+	return append(SearchModesExactWords(), []SearchMode{
+		{
+			ModeValue:    SearchModeRegexp,
+			TooltipTrKey: "search.regexp_tooltip",
+			TitleTrKey:   "search.regexp",
+		},
+	}...)
+}