Updated tokenizer to better matching when search for code snippets (#32261)

This PR improves the accuracy of Gitea's code search. 

Currently, Gitea does not consider statements such as
`onsole.log("hello")` as hits when the user searches for `log`. The
culprit is how both ES and Bleve are tokenizing the file contents (in
both cases, `console.log` is a whole token).

In ES' case, we changed the tokenizer to
[simple_pattern_split](https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-simplepatternsplit-tokenizer.html#:~:text=The%20simple_pattern_split%20tokenizer%20uses%20a,the%20tokenization%20is%20generally%20faster.).
In such a case, tokens are words formed by digits and letters. In
Bleve's case, it employs a
[letter](https://blevesearch.com/docs/Tokenizers/) tokenizer.

Resolves #32220

---------

Signed-off-by: Bruno Sofiato <bruno.sofiato@gmail.com>

modules/indexer/code/indexer_test.go

@@ -181,6 +181,55 @@ func testIndexer(name string, t *testing.T, indexer internal.Indexer) {
 					},
 				},
 			},
+			// Search for matches on the contents of files regardless of case.
+			{
+				RepoIDs: nil,
+				Keyword: "dESCRIPTION",
+				Langs:   1,
+				Results: []codeSearchResult{
+					{
+						Filename: "README.md",
+						Content:  "# repo1\n\nDescription for repo1",
+					},
+				},
+			},
+			// Search for an exact match on the filename within the repo '62' (case insenstive).
+			// This scenario yields a single result (the file avocado.md on the repo '62')
+			{
+				RepoIDs: []int64{62},
+				Keyword: "AVOCADO.MD",
+				Langs:   1,
+				Results: []codeSearchResult{
+					{
+						Filename: "avocado.md",
+						Content:  "# repo1\n\npineaple pie of cucumber juice",
+					},
+				},
+			},
+			// Search for matches on the contents of files when the criteria is a expression.
+			{
+				RepoIDs: []int64{62},
+				Keyword: "console.log",
+				Langs:   1,
+				Results: []codeSearchResult{
+					{
+						Filename: "example-file.js",
+						Content:  "console.log(\"Hello, World!\")",
+					},
+				},
+			},
+			// Search for matches on the contents of files when the criteria is part of a expression.
+			{
+				RepoIDs: []int64{62},
+				Keyword: "log",
+				Langs:   1,
+				Results: []codeSearchResult{
+					{
+						Filename: "example-file.js",
+						Content:  "console.log(\"Hello, World!\")",
+					},
+				},
+			},
 		}
 
 		for _, kw := range keywords {