fix(path): handle lowercasing that changes path length in windows relative()

[Punisheroot]

Summary

• Fix relative() from @std/path/windows dropping leading characters when a
  path contains a character that changes length when lowercased, such as İ
  (U+0130).
• Fall back to a segment-by-segment comparison whenever lowercasing changes the
  length of either resolved path.

Context

relative() lowercases both paths to compare them case-insensitively, then
slices the original to path using indexes found in the lowercased strings.
"İ".toLowerCase() is "i̇", which is two code units, so each such character in
the common prefix shifts those indexes and the result loses one leading
character per occurrence:

relative("C:\\İPTV\\player", "C:\\İPTV\\player\\src\\main.ts");
// "rc\\main.ts" instead of "src\\main.ts"

This also affects ESLint on Windows: @eslint/config-array uses this function
to match ignore patterns against paths relative to the config folder, so
projects under a directory containing İ stop matching **/node_modules/ and
end up linting all of node_modules.

The fallback mirrors the fix merged upstream for path.win32.relative() in
nodejs/node#53991.

Fixes #7336

Changes

• path/windows/relative.ts: when fromOrig/toOrig change length after
  toLowerCase(), compare path segments instead of using indexes computed on
  the lowercased strings.
• path/relative_test.ts: add regression cases with İ ported from
  path: fix relative on Windows nodejs/node#53991 plus the scenarios from path: relative() on Windows drops leading characters when a path contains "İ" #7336, and a ß control case.

Validation

• deno test -A path/: PASS (91 passed, 0 failed)
• deno test path/relative_test.ts: PASS (fails before the fix with
  ode_modules\\zod\\index.ts)
• deno check path/windows/relative.ts path/relative_test.ts: PASS
• deno lint path/windows/relative.ts path/relative_test.ts: PASS
• deno fmt --check: PASS
• deno doc --lint path/windows/relative.ts: PASS
• deno check --config browser-compat.tsconfig.json path/windows/relative.ts:
  PASS
• Full deno task test run locally on Windows: 7424 passed, 156 ignored; the
  35 failures are all fs/* symlink tests failing with os error 1314 (symlink
  privileges unavailable on this machine), unrelated to this change.
• deno task lint:docs and deno task test:browser can't run as-is on this
  Windows machine (command-line length limit and missing grep/xargs); the
  targeted equivalents above pass and CI covers the full tasks.

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.04%. Comparing base (f834d02) to head (c286abb).

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #7337    +/-   ##
========================================
  Coverage   95.04%   95.04%            
========================================
  Files         619      619            
  Lines       52012    51788   -224     
  Branches     9450     9414    -36     
========================================
- Hits        49434    49223   -211     
+ Misses       2031     2022     -9     
+ Partials      547      543     -4     

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[tomas-zijdemans]

This looks good. I noticed that Patch coverage is 67.74%

Could you investigate raising it? (ideally over 95% if practically possible)

[Punisheroot]

@tomas-zijdemans done!