Improve CreateMappings.ps1

## Description
Inspired by the issue https://github.com/Azure/azure-powershell/issues/10613

It is found that CreateMappings.ps1 generates help file to alias mapping using CreateMappings_rules.json.
It searches for the keywords of different rules in help file's path and file, if any match, choose a best one.

When more than one rules are hit, the current solution is ordering rule according to priority in CreateMappings_rules.json and selecting the first matched rule in CreateMappings.ps1.

The problem is if it is impossible to prioritize two rules how to handle the case.
Here is a example case.
Get-AzComputedNetworkxxxxx
Rule1: Compute
Rule2 :Network
Which rule should be applied to the case?
## Cost

Review CreateMappings.ps1 and CreateMappings_rules.json to understand how help-file paths and contents are matched and how priority is applied. Trace the example with both Compute and Network matches, then determine and document the intended handling for rules that cannot be prioritized; the mapping process should produce a defined, consistent result for such cases.

Written by the indexing model from the issue text.