Fix suffix * handling in our CODEOWNERS path matcher

[konrad-jamrozik]

As in subject. Prompted by this comment thread:

• Add path erroneously removed from CODEOWNERS azure-sdk-for-python#28539 (comment)

There were some other issues with the matcher being inconsistent with GitHub's matcher. For details, please see this comment:

• Fix suffix * handling in our CODEOWNERS path matcher #5308 (comment)

This PR contributes to:

• Add support for wildcard handling of file matching in codeowners library #2770

[konrad-jamrozik]

@weshaggard I made some significant changes since you approved; turns out, GitHub's CODEOWNERS matching logic is a bit inconsistent when it comes to handling suffixes. I did manual tests using my own scratchpad repo to confirm its behavior. The behavior is explained here.

In a nutshell:

• For top level dir, / doesn't work. One has to use /**.
• But for nested dirs, / works. I.e. one can write /foo/ and it is equivalent to /foo/**.
• * has different interpretations. If used with preceding slash, like /* or /foo/*
  it means "things only in this dir". But when used as a suffix, it means "anything".
  So /foo* is effectively /foo*/** OR /foo*. Where * in the OR clause
  should be interpreted as "any character except /".