Auto merge of #110655 - ChrisDenton:read-to-end, r=joshtriplett

Limit read size in `File::read_to_end` loop

Fixes #110650.

Windows file reads have perf overhead that's proportional to the buffer size. When we have a reasonable expectation that we know the file size, we can set a reasonable upper bound for the size of the buffer in one read call.

Author: bors