tidy-up: TEXT() vs _TEXT() vs _T() use (Windows)

[vszakats]

Use _TEXT() when interacting with CRT functions (also prefer over
synonym _T()), TEXT() for Win32 functions.

Within curl, they mean the same because CRT/Win32 Unicode mode are
always enabled in sync.

Ref: https://devblogs.microsoft.com/oldnewthing/20040212-00/?p=40643/

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I'm not firmly for _TEXT() over _T(). Just assumed the former is the
official macro based on Raymond not knowing about the short form. We
may stick with the short one, less symmetry, rarer, less greppable, but
shorter. Altogether rarely used in the code.

[Copilot]

Pull request overview

This PR standardizes Windows TCHAR literal macros to better reflect intent: _TEXT() (preferred over _T()) is used alongside CRT _tcs* functions, while TEXT() remains for Win32 API interactions, aligning with common Windows guidance.

Changes:

• Replaced _T() with _TEXT() in src/tool_main.c for a CRT _tcscmp() comparison.
• Replaced TEXT() with _TEXT() in Schannel and SSPI CRT string parsing/comparison code.
• Updated a Windows path-prefix check in lib/curlx/fopen.c to use _TEXT().

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/tool_main.c	Uses _TEXT() for the CRT _tcscmp() option check on Windows.
lib/vtls/schannel.c	Uses _TEXT() for CRT _tcs* parsing of certificate store location strings.
lib/curlx/fopen.c	Uses _TEXT() for the CRT _tcsncmp() check of the \\?\ path prefix.
lib/curl_sspi.c	Uses _TEXT() for CRT _tcschr() parsing and empty-string literals in SSPI identity creation.

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[jay]

Any is fine, I've seen all of them used, most projects will define _UNICODE and UNICODE together for Unicode, so even though _T isn't technically the same it's effectively the same.