[lldb][meta] Support building and embedding LLDB under Emscripten

Meta-issue to track the work required to build and embed LLDB under an Emscripten host.

This is related to, but distinct from #150449. That issue tracks LLDB support for debugging WebAssembly targets. This issue tracks LLDB itself running under Emscripten—for example, embedding `liblldb`, LLDB's command interpreter and
`lldb-dap` inside a browser application such as [WasmBolt](https://github.com/anutosh491/WasmBolt) (try [here](https://anutosh21.github.io/WasmBolt/))

## Current prototype

The browser-hosted prototype can currently:

- build and load `liblldb` under Emscripten;
- inspect Wasm symbols, DWARF source information and disassembly through the
SB API;
- connect LLDB's existing `ProcessWasm` support to an in-process WAMR runtime;
- set breakpoints, inspect local variables, step and continue;
- drive the same session through LLDB's command interpreter and `lldb-dap`.

These experiments are currently downstream prototypes. The patches below are intended to make the underlying LLDB build and host abstractions cleanly support this use case upstream. See demos below

https://github.com/user-attachments/assets/ff73f87f-0f9e-422a-aaba-5af6daa4bbb1

https://github.com/user-attachments/assets/2e35e88e-142c-4b69-a40c-5a943ead158c

## Upstream patch series

The patches should be reviewed and merged in this order:

- [x] #223169 — `[lldb] Add HostInfoEmscripten`
- [x] #223200 — `[lldb] Add PlatformEmscripten`
- [x] #223206 — `[lldb] Support building lldbHost under Emscripten`
- [ ] #223210 — `[lldb] Add an option to build liblldb statically`

#223162 was the initial bootstrap that selected `PlatformLinux` as the Emscripten host platform. It is superseded by the dedicated
`HostInfoEmscripten` and `PlatformEmscripten` split above and is not intended to remain part of the final series.

Start by reading the four upstream issues in the listed order: #223169, #223200, #223206, and #223210. Use the prototype description and each issue's proposed patch as the entry points; the meta-issue is complete when the Emscripten host and platform support, lldbHost build, and static liblldb option are upstreamed.

Written by the indexing model from the issue text.