fs: adjust `position` validation in reading methods

This PR:

• Adds validation of position argument to filehandle.read(), same as in cousin methods
• Allows bigint position for filehandle.read()
• Adjusts min number position from Number.MIN_SAFE_INTEGER to -1
• Adjusts min bigint position from -2⁶³ to -1
• Adjusts max bigint position from 2⁶³ - 1 to 2⁶³ - 1 - length
• Makes docs a bit more pedantic

Tests are still passing and documented features are still working, but there are potentially breaking changes:

• When user passes an unsafe number or not a number in filehandle.read(), an exception is thrown.
  • Previously: silently read from current position.
• When user passes a safe bigint in filehandle.read(), it works.
  • Previously: silently read from current position.
• When user passes a negative integer (except for -1 or -1n which explicitly means current position), an exception is thrown.
  • Previously: silently read from current position.
• When user passes a bigint close to upper limit (2⁶³ - 1), and adding length breaks this limit, an exception is thrown.
  • Previously: EINVAL from read(2) (platform-dependent)