vlib,tools: add an arrays.diff module, implement a simple platform independent tool v diff file1.txt file2.txt using it (#24428)

cmd/tools/vdiff.v

@@ -0,0 +1,37 @@
+import os
+import flag
+import term
+import arrays.diff
+
+fn main() {
+	mut fp := flag.new_flag_parser(os.args[1..])
+	fp.application('v diff')
+	fp.version('0.0.1')
+	fp.description('Compare files line by line. Example: `v diff examples/hello_world.v examples/log.v`')
+	fp.arguments_description('file1 file2')
+	fp.skip_executable()
+	fp.limit_free_args_to_at_least(2)!
+
+	if fp.bool('help', `h`, false, 'Show this help screen.') {
+		println(fp.usage())
+		exit(0)
+	}
+
+	args := fp.finalize() or {
+		eprintln('Argument error: ${err}')
+		exit(1)
+	}
+
+	src := os.read_lines(args[0])!
+	dst := os.read_lines(args[1])!
+	mut ctx := diff.diff(src, dst)
+	patch := ctx.generate_patch(
+		colorful:     term.can_show_color_on_stdout()
+		block_header: true
+		unified:      3
+	)
+	if patch.len > 0 {
+		print(patch)
+		exit(1)
+	}
+}

cmd/v/v.v

@@ -24,6 +24,7 @@ const external_tools = [
 	'complete',
 	'compress',
 	'cover',
+	'diff',
 	'doc',
 	'doctor',
 	'download',