As per https://tc39.es/ecma262/#sec-hostimportmoduledynamically defined,
referencingScriptOrModule in HostImportModuleDynamically can be a Script
Record, a Module Record, or null.
So to https://tc39.es/proposal-shadowrealm/#sec-shadowrealmimportvalue,
the HostImportModuleDynamicallyCallback is been invoked with a `null`
resource_name. This may not be considered a breaking change as the
parameter resource_name is defined as Local<Value>.

Updates d8's DoHostImportModuleDynamically to handle null resource_name,
and resolve the dynamically imported specifier relative to the executing
script's origin. In this way, we have to set ModuleEmbedderData.origin
even if the JavaScript source to be evaluated is Script. Also, a
ModuleEmbedderData is created for each ShadowRealm to separate their
module maps from the initiator context's.

Bug: v8:11989
Change-Id: If70fb140657da4f2dd92eedfcc4515211602aa46
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3522883Reviewed-by: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Chengzhong Wu <legendecas@gmail.com>
Cr-Commit-Position: refs/heads/main@{#80118}