Consolidate the two cookie parsers `parseCookie` and `parseCookieHeader`

parseCookie (used by filterCookies for event cookie records) and parseCookieHeader (used by httpHeadersToSpanAttributes for span attributes) have several differences:

• Nameless segments: filterCookies('opaque-blob; theme=dark', true) returns {theme: 'dark'} and drops the blob silently. The span attribute shows ['[Filtered]', 'theme=dark'].
• Set-Cookie attributes: filterCookies('sid=1; Max-Age=3600; Path=/', true) returns {sid: '[Filtered]', 'Max-Age': '3600', Path: '/'}. Max-Age and Path are metadata, not cookies. parseCookieHeader strips them.
• Only parseCookie URL-decodes values and strips quotes.

One parser returning ordered [name, value][] pairs, with a Set-Cookie mode, could work at both call sites. filterCookies.test.ts has two it.fails tests pinning the intended Set-Cookie behavior -> those need to be flipped when fixed.

Out of the #24090 review: https://github.com/getsentry/sentry-javascript/pull/24090#discussion_r4041421140 and https://github.com/getsentry/sentry-javascript/pull/24090#discussion_r4041448119.