PluginApplicationBuildProgressCrossVersionSpec.groovy

This commit introduces a new `OperationType.PROJECT_CONFIGURATION` and

adds specific `ProgressEvent` implementations. When the operation type

is not requested, no progress configuration events (neither as typed

events nor as generic build operations) will be reported. While that

will remove generic progress configuration events and their children

from clients that use old TAPI versions against Gradle >= 5.1, it is

consistent with the behavior for tasks and work items.

We've been bitten by external repository fluctuation for a long time.

This PR makes most of tests use repository mirrors set up by ourselves

via init script and system property.

There're still some tests not switching to mirrors, which would be fixed

in follow-up commits.

See https://github.com/gradle/gradle-private/issues/1341

and https://github.com/gradle/gradle/issues/5777

Recover these tests after jfrog adjusted their cipher configuration

Remote URLs are also supported:

```

plugins {

script "path/to/other.gradle"

script "https://example.com/another.gradle"

}

```

Local file paths are expressed as relative from the requesting script.

Constrain plugins {} block api to distinguish binary and script

plugin requests by both strongly modeled types and ad-hoc groovy parsing

of the plugins block. This pave the way for proper support of the

plugins {} block with the Gradle Kotlin DSL.

Implement ScriptPlugin PluginResolver by generating a synthetic

"imperative" Plugin class that loads and applies the script plugin when

applied.

This synthetic generated loader class and the script plugins are loaded

into the buildSrc classloader scope.

Only Project targets are supported.

`apply false` is not supported.