trivial: Style libelf

libelf: remove duplicate and add missing functions

By normalising return types, most functions in `elfxx.c` can be merged and
moved into `elf.c`.

Also add missing prototypes and functions for accessing ELF fields.
- getSectionStringTableIndex
- getSectionNameOffset
- getSectionOffset
- getSectionLink
- getSectionInfo
- getSectionAddrAlign
- getSectionEntrySize

libelf: normalise types

Use size_t and uintptr_t where appropriate.
Add enum elf_addr_type for physical/virtual memory.

libelf: delete struct definitions

These definitions are also provided by musllibc or newlib.

libelf: introduce memory safety

The size of the buffer containing the ELF file needs to be known to
access it safely.

Change all public void * references to elf_t *, which requires a size
parameter.

libelf: re-order functions

Re-order functions based on purpose and ELF header location.

libelf: delete unnecessary functions

This deletes:

elf_getProgramHeaderInfo: This is an awkward convenience function that
appears to be unused.

elfxx_getProgramSegmentTable,
elfxx_getSegmentType: Functions with different names but the same
functionality already exist.

elfxx_getSegmentInfo: Both of the above.

libelf: normalise indents and whitespace

pragma once and for all

SELFOUR-1083 optionally return section ID in elf_getSectionNamed

libelf: Implement helpers for retrieving alignment

The program headers have helpers for retrieving every value except the alignment,
this commit adds a helper for that.

Remove trailing whitespace

libelf: Qualify some const char * parameters.