avoid creating unnecessary owned strings & fix limits

[rajveermalviya]

Changes

• added support for advertising maxBindingsPerBindGroup limt
• use smallvec crate to avoid possible heap allocations, mimics what wgpu-rs already does for these functions:
  • wgpuQueueSubmit
  • wgpuRenderPassEncoderExecuteBundles
  • wgpuQueueSubmitForIndex
• replace OwnedLabel with some helper functions for *const c_char
  • ptr_into_label: replaces general usages of OwnedLabel, it creates a Cow::Borrowed of &str which avoids unnecessary heap allocation of String. Only some functions in wgpu-core converts the passed Cow::Borrowed of &str to owned String.
  • ptr_into_path & ptr_into_pathbuf are just similar helpers.