feat: support custom esbuild module path

[mrgrain]

Fixes #218

This feature is required to unblock users of non-TypeScript languages. It can also be used to set different versions of esbuild for each Construct.

Custom path can be set on CodeProps and TransformerProps per instance:

const props = {
  esbuildModulePath: '/path/to/global/esbuild/module';
}

Alternatively, the path can be set globally using the CDK_ESBUILD_MODULE_PATH environment variable:

CDK_ESBUILD_MODULE_PATH="/path/to/global/esbuild/module" cdk synth

In TypeScript, the property defaults to 'esbuild'.

All other languages will use an automatic "best effort" resolution mechanism. The exact algorithm for this is considered an implementation detail and will change in future as new heuristics are added. Specifically, the package might be installed dynamically to a temporary location. To opt-out of this behavior, set esbuildModulePath prop or CDK_ESBUILD_MODULE_PATH env variable.

Python, Go, .NET and Java should use an absolute path, because the jsii execution environment uses a temporary working directory.