Added Active SSTI Razor BCheck

[alp1n3-eth]

Checks for the evaluation of arithmetic in server-side template injection scenarios using Razor (ASP.NET). The BCheck will insert a payload using the Razor syntax @() and if the evaluated output is seen in the response it will trigger and report the issue.

BCheck Contributions

• BCheck compiles and executes as expected
• BCheck contains appropriate metadata (name, version, author, description and appropriate tags)
• Only .bcheck files have been added or modified
• BCheck is in the appropriate folder
• PR contains single or limited number of BChecks (Multiple PRs are preferred)
• BCheck attempts to minimize false positives