Change how wasm DWARF is inserted into artifacts (#5358)

This commit fixes a bug with components by changing how DWARF
information from a wasm binary is copied over to the final compiled
artifact. Note that this is not the Wasmtime-generated DWARF but rather
the native wasm DWARF itself used in backtraces.

Previously the wasm dwarf was inserted into sections `.*.wasm` where `*`
was `debug_info`, `debug_str`, etc -- one per `gimli::SectionId` as
found in the original wasm module. This does not work with components,
however, where modules did not correctly separate their debug
information into separate sections or otherwise disambiguate. The fix in
this commit is to instead smash all the debug information together into
one large section and store offsets into that giant section. This is
similar to the `name`-section scraping or the trap metadata section
where one section contains all the data for all the modules in a component.

This simplifies the object file parsing by only looking for one section
name and doesn't add all that much complexity to serializing and looking
up dwarf information as well.

crates/environ/src/obj.rs

@@ -119,3 +119,12 @@ pub const ELF_WASMTIME_INFO: &'static str = ".wasmtime.info";
 /// sometimes quite large (3MB seen for spidermonkey-compiled-to-wasm), can be
 /// paged in lazily from an mmap and is never paged in if we never reference it.
 pub const ELF_NAME_DATA: &'static str = ".name.wasm";
+
+/// This is the name of the section in the final ELF image that contains the
+/// concatenation of all the native DWARF information found in the original wasm
+/// files.
+///
+/// This concatenation is not intended to be read by external tools at this time
+/// and is instead indexed directly by relative indices stored in compilation
+/// metadata.
+pub const ELF_WASMTIME_DWARF: &str = ".wasmtime.dwarf";