Separate compilation and linker phases (#376)

Separate between compilation and linker phases to allow deploy time
linking and back-porting era compiler changes to fix #91. Unlinked
contract binaries (caused by missing libraries or missing factory
dependencies in turn) are emitted as raw ELF object.

Few drive by fixes:
- #98
- A compiler panic on missing libraries definitions.
- Fixes some incosistent type forwarding in JSON output (empty string
vs. null object).
- Remove the unused fallback for size optimization setting.
- Remove the broken `--lvm-ir`  mode.
- CI workflow fixes.

---------

Signed-off-by: Cyrill Leutwiler <bigcyrill@hotmail.com>
Signed-off-by: xermicus <bigcyrill@hotmail.com>
Signed-off-by: xermicus <cyrill@parity.io>

crates/common/src/extension.rs

@@ -37,4 +37,4 @@ pub static EXTENSION_POLKAVM_ASSEMBLY: &str = "pvmasm";
 pub static EXTENSION_POLKAVM_BINARY: &str = "pvm";
 
 /// The ELF shared object file extension.
-pub static EXTENSION_SHARED_OBJECT: &str = "so";
+pub static EXTENSION_OBJECT: &str = "o";