Add initial support for code metadata (#1840)

See https://github.com/WebAssembly/tool-conventions/blob/main/CodeMetadata.md  for the specification.

In particular this pr implements the following:

- Parsing code metadata sections in BinaryReader, providing appropriate callbacks that a BinaryReaderDelegate can implement:
    - BinaryReaderObjdump: show the sections in a human-readable form
    - BinaryReaderIr: add code metadata in the IR as expressions
- Parsing code metadata annotations in text format, adding them in the IR like the BinaryReaderIR does
- Writing the code metadata present in the IR in the proper sections when converting IR to binary
- Support in wasm-decompiler for showing code metadata as comments in the pseudo-code

All the features have corresponding tests.

Support for code metadata is gated through the --enable-code-metadata feature. For reading/writing in the text format, --enable-annotations is also required.

Missing features:

    Support for function-level code metadata (offset 0)
    Extensive validation in validator.cc (like making sure that all metadata instances are at the same code offset of an instruction)

1 files changed, 43 insertions, 0 deletions

diff --git a/test/dump/code-metadata.txt b/test/dump/code-metadata.txt
new file mode 100644
index 00000000..1b2254d7
--- /dev/null
+++ b/test/dump/code-metadata.txt
@@ -0,0 +1,43 @@
+;;; TOOL: run-objdump
+;;; ARGS0: --enable-annotations --enable-code-metadata
+;;; ARGS1: --headers --details
+(module
+  (func $f (param i32) (result i32)
+    i32.const 1234
+    local.get 0
+    (@metadata.code.test "aa\01a") i32.add
+    return))
+(;; STDOUT ;;;
+
+code-metadata.wasm:	file format wasm 0x1
+
+Sections:
+
+     Type start=0x0000000a end=0x00000010 (size=0x00000006) count: 1
+ Function start=0x00000012 end=0x00000014 (size=0x00000002) count: 1
+   Custom start=0x00000016 end=0x00000032 (size=0x0000001c) "metadata.code.test"
+     Code start=0x00000034 end=0x0000003f (size=0x0000000b) count: 1
+
+Section Details:
+
+Type[1]:
+ - type[0] (i32) -> i32
+Function[1]:
+ - func[0] sig=0
+Custom:
+ - name: "metadata.code.test"
+   - func[0]:
+    - meta[6]:
+     - 0000000: 6161 0161                                aa.a
+Code[1]:
+ - func[0] size=9
+
+Code Disassembly:
+
+000036 func[0]:
+ 000037: 41 d2 09                   | i32.const 1234
+ 00003a: 20 00                      | local.get 0
+ 00003c: 6a                         | i32.add
+ 00003d: 0f                         | return
+ 00003e: 0b                         | end
+;;; STDOUT ;;)