Refactor highlight and diff (#36599)

1. fix a performance regression when using line-by-line highlighting
* the root cause is that chroma's `lexers.Get` is slow and a lexer cache
is missing during recent changes
2. clarify the chroma lexer detection behavior
* now we fully manage our logic to detect lexer, and handle overriding
problems, everything is fully under control
3. clarify "code analyze" behavior, now only 2 usages:
* only use file name and language to detect lexer (very fast), mainly
for "diff" page which contains a lot of files
* if no lexer is detected by file name and language, use code content to
detect again (slow), mainly for "view file" or "blame" page, which can
get best result
4. fix git diff bug, it caused "broken pipe" error for large diff files

modules/git/gitcmd/command.go

@@ -306,6 +306,10 @@ func (c *Command) MakeStdinPipe() (writer PipeWriter, closer func()) {
 // MakeStdoutPipe creates a reader for the command's stdout.
 // The returned closer function must be called by the caller to close the pipe.
 // After the pipe reader is closed, the unread data will be discarded.
+//
+// If the process (git command) still tries to write after the pipe is closed, the Wait error will be "signal: broken pipe".
+// WithPipelineFunc + Run won't return "broken pipe" error in this case if the callback returns no error.
+// But if you are calling Start / Wait family functions, you should either drain the pipe before close it, or handle the Wait error correctly.
 func (c *Command) MakeStdoutPipe() (reader PipeReader, closer func()) {
 	return c.makeStdoutStderr(&c.cmdStdout)
 }