RSRP-46310: New code suggestion: "Check if has key" (for dictionaries, akin to "Check if is null")

Much like the "Check if is null" code suggestion, a "Check if has key" suggestion, invoked in an expression invoking the indexer of a dictionary:

Given the following code:

    Dictionary<string,string> dict;
    string value = dict["mykey"];

If the user invoked the "Check if has key" code suggestion, then the following code would be generated:

    Dictionary<string,string> dict;

    if (dict.ContainsKey("mykey"))
    {
        string value = dict["mykey"];
    }