Resolves #6
Resolves #33
Resolves #35

Sure ideally we can start with an mkdist-compatible context API for custom extensions in transpiler.

Originally posted by @pi0 in #6

I made this as a starting point for further discussions about #6, it's mainly based on the mkdist loaders.

New features in this PR:

Plugin support for transform entries.

Plugin monorepo will be available here soon: https://github.com/unjs/obuild-plugins
Until the packages are not published, they are packed and resolved from the /plugins dir in this PR.

Possible setup:

 {
    type: "transform",
    input: "src/",
    outDir: "dist/",
    plugins: [
      oxcDts({ force: true }), // Force generate, skip emitting a file if isolatedDeclarations fails
      tsgoDts(), // Reuse .d.(m)ts from `oxc-dts` and generate for TS files that `oxc-dts` could not work on
      vueTscDts(), // Reuse .d.(m)ts from `oxc-dts` and `tsgo-dts` and generate only for Vue files
      vueSFCTransformer(), // Transform Vue SFCs
      oxcTransform(), // Transform others
      sass(),
      postcss(),
    ],
  }

Plugins have a transform() method, we call these recursively in the order that is provided in the configuration.

• if it returns with an array of files, we go through each file and try to call the next plugins transform method with it
• if it returns undefined we go to the next plugin

Plugins can also have temp. storage assigned to them for each entry context. This is useful when you for example define the plugins once and use them for multiple entries with the same configuration.

TS Config resolution

On build start we find and resolve all paths in the TS Config to absolute paths based on where the actual configuration coming from. (TS config entries can also be added into the transform entries).
Later the transform plugins can use these to make relative paths based on their requirements.

Source map serialization/path rewrite

The plugins don't have enough context to know where each file will be written to, this is done here.
Added mapDir config option to write these separately. (This directory is not cleaned on each build automatically)

declarationDir support

When provided in TS config, the declarations are written in the provided directory (This directory is not cleaned on each build automatically)