Motivation:

We can replace some "hand-rolled" integer checks with our own static utility method to simplify the code.

Modifications:

Use methods provided by `ObjectUtil`.

Result:

Cleaner code and less duplication

Compared against 4.1.25.6.dse, this tag cherry-picks upstream commits
that fixed bugs in HttpObjectDecoder/HttpRequestDecoder, plus two
intermediate refactoring commits that indirectly affect those bugfix
commits.

What follows is a list of PR links, issue links, CVE links, and hashes
associated with the cherry-picked commits.

Verify we do not receive multiple content-length headers or a content-length and transfer-encoding: chunked header when using HTTP/1.1 (netty#9865)
	https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-7238
	netty#9861
	netty#9865

	8494b04

Detect missing colon when parsing http headers with no value (netty#9871)
	GHSA-cqqj-4p63-rrmm
	netty#9866
	netty#9871

	a7c18d4

Fix typos in javadocs (netty#9527)
	skipped

Correctly handle whitespaces in HTTP header names as defined by RFC7230#section-3.2.4 (netty#9585)
	https://nvd.nist.gov/vuln/detail/CVE-2019-16869
	netty#9571
	netty#9585

	39cafcb

Use `AppendableCharSequence.charAtUnsafe(int)` in `HttpObjectDecoder` (netty#9492)
	netty#9492

	85fcf4e

use checkPositive/checkPositiveOrZero (netty#8835)
	netty#8835

	4c64c98

HttpObjectDecoder ignores HTTP trailer header when empty line is rece… (netty#8799)
	netty#8736
	netty#8799

	91d3920