GPU assembly: fix potential basis loading offset error

Use CeedMallocArray for void pointers in CUDA/HIP QFunctionContext

Use backend functions for SyncArray in CUDA and HIP

gpu - remove 'quoted' operator assembly kernels

jit - add interface for adding additional jit source dirs

move include/ceed-jit-source to include/ceed/jit-source

jit - use relpath from include/ceed-jit-source for jit source files

tidy - small tidy fixes

Merge pull request #920 from CEED/jeremy/conversion

Explicit casting of vector sizes

gpu - fix error handling in size conversion

Merge pull request #925 from CEED/gpu-assemble

Add some matrix assembly support to GPU backends

Add fallback kernel for larger element sizes in GPU assembly

Add LinearAssemble CUDA reference implementation for low-order elements

minor - explicit casting of vector sizes

minor - update copyright headers

rstr - use CeedSize for l_size

vec - use CeedSize for vector lengths

qf - extend ctx read/write feature to qf

ctx - add read-only access for QFContext

vec/ctx - make backend restore function optional

gpu - style consistency

gpu - minor style

gpu - improved human-readability of debugging output

gpu - pull quoted kernels into separate files

style - consistent nameing and style for gpu backends