escape: replace Curl_isunreserved with ISUNRESERVED
- Use the ALLCAPS version of the macro so that it is clear a macro is
being called that evaluates the variable multiple times.
- Also capitalize macro isurlpuntcs => ISURLPUNTCS since it evaluates
a variable multiple times.
This is a follow-up to 291d225a which changed Curl_isunreserved into an
alias macro for ISUNRESERVED. The problem is the former is not easily
identified as a macro by the caller, which could lead to a bug.
For example, ISUNRESERVED(*foo++) is easily identifiable as wrong but
Curl_isunreserved(*foo++) is not even though they both are the same.
Closes https://github.com/curl/curl/pull/11846