Do not check maximum image size while merely parsing the file. Do the test when actually decoding the image (#1220)

Fixes compiler errors like the following with clang-12:

/path/to/libheif/libheif/api/libheif/heif.cc:1673:10: error: result of comparison of constant 4294967295 with expression of type 'uint16_t' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
      cp > std::numeric_limits<std::underlying_type<heif_color_primaries>::type>::max()) {
      ~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/path/to/libheif/libheif/api/libheif/heif.cc:1714:10: error: result of comparison of constant 4294967295 with expression of type 'uint16_t' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
      tc > std::numeric_limits<std::underlying_type<heif_transfer_characteristics>::type>::max()) {
      ~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/path/to/libheif/libheif/api/libheif/heif.cc:1751:10: error: result of comparison of constant 4294967295 with expression of type 'uint16_t' (aka 'unsigned short') is always false [-Werror,-Wtautological-constant-out-of-range-compare]
      mc > std::numeric_limits<std::underlying_type<heif_matrix_coefficients>::type>::max()) {
      ~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3 errors generated.

Add convenience bindings for javascript to check filetype and to get primary image handle 

copy DLL whenever the was rebuilt (not whenever the EXE was rebuilt), and only copy when using shared libraries

Fix unsigned integer

doxygen: minor updates