[Fixes #174] implement no-shadowed-variable converter

[alejo90]

PR Checklist

• Addresses an existing issue: fixes Missing converter: no-shadowed-variable #174
• That issue was marked as status: accepting prs

Overview

I added a converter between tslint's no-shadowed-variable rule and eslint's no-shadow rule. Tslint's no-shadowed-variable's default behavior corresponds to eslint's no-shadow with the hoist option set to all. no-shadow's host option can be switched to never when tslint's no-shadowed-variable has a configuration object with temporalDeadZone set to false.
If no-shadowed-variable is configured to disable checking for underscore, a notice is shown explaining that eslint does not support disabling checking on whether a variable name starts with underscore or not and asking users to use no-shadow's allow config instead, if they want to disable checking for specific variables.
Finally, if no-shadowed-variable is set to disable checks for anything other than temporalDeadZone and underscore (e.g. class, function, etc.), a notice saying that eslint doesn't support disabling checks based on declaration type is shown.

Reference:

• no-shadowed-variable
• no-shadow

[JoshuaKGoldberg]

Amusing differences in rule settings. Thanks!