feature: add rule for trojan source

[kfess]

Description

Add rule to detect Trojan Source attacks (CVE-2021-42574) using bidirectional Unicode control characters as G116.

The rule scans entire file content to detect dangerous bidirectional text control characters:

RLO (U+202E), LRI/RLI/FSI (U+2066/2067/2068), LRE/RLE (U+202A/202B), PDF (U+202C), LRO (U+202D), RLM/LRM (U+200F/200E)

References:

• https://trojansource.codes/trojan-source.pdf
• https://www.compart.com/en/unicode/U+200f
• https://www.compart.com/en/unicode/U+200e

Fixes

Issue: #1429

Comment

testutils/g116_samples.go uses #nosec because G116 scans entire file content (not just AST nodes but also comments). The test file contains actual bidirectional Unicode characters to verify detection works correctly. Without #nosec, gosec would flag its own test samples when running make test.

[ccojocar]

Does this perform well with large files?

I would use something like to make sure that we don't run out of memory and have performance issues:

file, err := os.Open("")
if err != nil {
    log.Fatal(err)
}
defer file.Close()
scanner := bufio.NewScanner(file)
for scanner.Scan() {
    line := scanner.Text()
    // Process line
}
if err := scanner.Err(); err != nil {
    log.Fatal(err)
}

[ccojocar]

Please can you rebase this pull request? Thanks