Improve CLEAR_MODES docs

[ivanpopelyshev]

As discussed with @SukantPal , I have to clarify this once more.

Most people that write filters dont know about clamping and other tricks that are needed in case we use pow2 temporary renderTextures. Even our BlurFilter is affected, @GoodBoyDigital wrote this version for v5 :)

For them, we distinguish two clearing modes - one CLEAR that clears everything, and second BLIT that just overwrites new content over texture, and leaves right and bottom zone as it was.

[ShukantPal]

@ivanpopelyshev BLIT mode doesn't not clear only the filtering area on the texture right now. If that was the intended purpose, we need to fix it.

[bigtimebuddy]

I find this doc change not particularly useful or legible. This need some editing for clarity.

[codecov-io]

Codecov Report

Merging #7075 (7b27585) into dev (3f04834) will not change coverage.
The diff coverage is n/a.

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[ShukantPal]

Hey @bigtimebuddy, I had a chat with @ivanpopelyshev and we cleared up (get it?) what CLEAR_MODES.BLIT should be doing. It basically skips clearing the filter texture if the filter has state.blend = false - as that will overwrite pixels anyway. Setting forceClear on the FilterSystem will make this mode clear regardless of the blend mode. That flag may be used in the future to force clearing on devices where that operation makes things faster.

[ShukantPal]

GitHub has a bug :(

[GoodBoyDigital]

lgtm 👍

[bigtimebuddy]

Thank you @SukantPal and @ivanpopelyshev for making this better.