Add support for $csp filter rules

[antonok-edm]

Easylist contains some rules with $csp options. These are useful as a last-resort when other more fine-grained blocking approaches are insufficient, and are implemented by modifying the Content-Security-Policy response headers from a document or subdocument request.

More details about the semantics of these options can be found on the uBlock Origin wiki and the AdGuard knowledgebase:

• https://github.com/gorhill/uBlock/wiki/Static-filter-syntax#csp
• https://kb.adguard.com/en/general/how-to-create-your-own-ad-filters#csp-modifier

[btlechowski]

Verification passed on

Brave	1.25.18 Chromium: 90.0.4430.72 (Official Build) nightly (64-bit)
Revision	b6172ef8d07ef486489a4b11b66b2eaeed50d132-refs/branch-heads/4430@{#1233}
OS	Ubuntu 18.04 LTS

Verified test plan from brave/brave-core#8281
Verified the scripts were blocked:

Refused to load the script '<URL>' because it violates the following Content Security Policy directive: "script-src 'self' 'unsafe-inline' <URL> *.hcaptcha.com". Note that 'script-src-elem' was not explicitly set, so 'script-src' is used as a fallback.

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Verified passed with

Brave | 1.25.60 Chromium: 90.0.4430.212 (Official Build) beta (x86_64)
-- | --
Revision | e3cd97fc771b893b7fd1879196d1215b622c2bed-refs/branch-heads/4430@{#1429}
OS | macOS Version 10.15.7 (Build 19H1030)

Verified test plan from brave/brave-core#8281 (comment).

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Verification passed on

Brave | 1.25.60 Chromium: 90.0.4430.212 (Official Build) beta (64-bit)
-- | --
Revision | e3cd97fc771b893b7fd1879196d1215b622c2bed-refs/branch-heads/4430@{#1429}
OS | Windows 10 OS Version 2004 (Build 19041.985)

• Verified the test plan from Update adblock-rust with CSP rule support brave-core#8281
  

[stephendonner]

@btlechowski is that the correct user-agent (1.23.71), as this is in the 1.25.x milestone?

[btlechowski]

Right, silly mistake. Fixed.

[srirambv]

Verification passed on the following devices running 1.25.51 x64 Beta build

• Verified test plan from Update adblock-rust with CSP rule support brave-core#8281

OnePlus (Android 10)	Samsung Tab A (Android 10)