Sd card usb presentation fixes

[dhalbert]

• Fixes SD card USB presentation problems #10632.
• Does not deal with write-locking problem with USB automount #10510, which touches some of the same code, but I'll put that in a separate PR after some further consultation.

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SD card USB presentation

• Add new .h-only compile option CIRCUITPY_SDCARD_USB, which will enable/disable presenting SD card as a USB MSC LUN.
• Enable on all ports except atmel-samd due to some bug that causes USB disconnection. I tested most of the other ports, and they don't have this problem. I'll open a separate issue about this for fixing post 10.0.0.

Prevent unneeded auto-reload

• Do not trigger an auto-reload if the host is doing a USB write that is not to the filesystem, but instead to the volume metadata (probably this is only the dirty bit being set/cleared). This prevents random long-interval auto-reloads (like 70 seconds) on Linux. macOS and Windows didn't have this problem. I check for this by seeing whether the LBA being written is below the FAT filesystem.

Technical debt found in passing

• Use gc_ptr_on_heap() instead of gc_nbytes() > 0 when checking if an object on the heap. Will be slightly faster.
• Reformatted some code with preprocessor guides around line 300 in supervisor/shared/usb/usb_msc_flash.c so the editor does not mess up the indentation.

[tannewt]

Minor things. Want to document this behavior somewhere? Maybe the workflow markdown?

[dhalbert]

Want to document this behavior somewhere? Maybe the workflow markdown?

I added a paragraph to the #### SD card drive section in workflows.md.

[tannewt]

One additional doc thing.

[tannewt]

Looks good! Thank you!