Add HttpValidationPolicy controlling semicolon delimitation of chunk-exts

Balsa currently accepts requests where `chunk-size` contains illegal whitespace (SP or HTAB). For example, Balsa parses an `1 A` chunk-size as `1` and the chunk extension as ` A`. This is slightly incorrect.

There are two primary cases to consider:

1. `chunk-size` followed by `chunk-ext` + `CRLF` framing
2. `chunk-size` followed only by `CRLF` framing

For `chunk-size` without a `chunk-ext`, any trailing `SP/HTAB` is always illegal.

For `chunk-size` with a `chunk-ext`, there actually is a case where it’s valid to have whitespace after `chunk-size`. If that `chunk-ext` begins with `BWS`, it is perfectly legal to have `SP` or `HTAB` following the `chunk-size`. However, that is legal if and only if, the `BWS` is part of a `chunk-ext` and not superfluous before a `CRLF`.

Unfortunately, Balsa does not have any enforcement that `chunk-ext` contain a `;` which makes it difficult to differentiate between the `SP` / `HTAB` being `BWS` in a chunk-ext or erroneous trailing whitespace so we add enforcement that the `chunk-ext` contains a `;` and, if it is present, it is only preceded by `SP` or `HTAB`.

Protected by unused http validation policy.

PiperOrigin-RevId: 874812254