Use dynamic allocation for ffmpeg fft tables on Windows.

[goodov]

This PR:

1. replaces static arrays with on-demand dynamic memory allocations.
2. reverts unnecessary 3.5MB allocations that has no observable effects on Chromium codebase. FFmpeg/FFmpeg@8f48a62. The patch [1/5] was discussed and landed here: https://patchwork.ffmpeg.org/project/ffmpeg/patch/[email protected]/

Other related patches around avutil/tx_template look fine and shouldn't break because of our revert:

[2/5] https://patchwork.ffmpeg.org/project/ffmpeg/patch/[email protected]/
[3/5] https://patchwork.ffmpeg.org/project/ffmpeg/patch/AS8P250MB074401A2AF976238F94F118B8F2C9@AS8P250MB0744.EURP250.PROD.OUTLOOK.COM/
[4/5] https://patchwork.ffmpeg.org/project/ffmpeg/patch/AS8P250MB0744B3A7C36BC043E7E56B388F2C9@AS8P250MB0744.EURP250.PROD.OUTLOOK.COM/
[5/5] https://patchwork.ffmpeg.org/project/ffmpeg/patch/AS8P250MB0744DF70DF80AEA5896DF0598F2C9@AS8P250MB0744.EURP250.PROD.OUTLOOK.COM/

The original issue is only reproducible on Windows, because Windows maps bss_seg to private memory even if the memory is not accessed. Linux on the other hand does the mapping only on memory access.

Resolves brave/brave-browser#35264

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run lint, npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

[goodov]

we cannot use chromium_src for this override, because tx_template.c is included into tx_float.c.

[atuchin-m]

Let's add the link to the FFmpeg discussion about adding these lines. this PR.
It's hard to find it from the paches blame.

[goodov]

it's added into description