New Rule: Lock objects should be read-only

[pavel-mikula-sonarsource]

As proposed by @Corniel here: https://community.sonarsource.com/t/new-rule-for-c-and-vb-net-locks-should-be-released/60951/2

Non-compliant

private object lock = new object(); // Noncompliant {{lock objects should be read-only.}}

Compliant

private readonly object lock = new object();

[pavel-mikula-sonarsource]

To distinguish between S2933 and this: This should trigger on fields used by lock and SyncLock statements.

[antonioaversa]

Seems to be a duplicate of #6701, implementation of https://sonarsource.github.io/rspec/#/rspec/S2445/csharp for C#