Fix bugs in XSD and SHACL schema files (v3.0.1)

[s-heppner]

This fixes two bugs found in schema files:

SHACL

Make SHACL regex patterns follow JSON Schema ones

We included the regex pattern as-is from the
input which caused problems with the
regex engines as the patterns in the meta-model
are written in a Python dialect
(and assuming that the regex engine works on
UTF-32 characters). However, most regex engines
in the wild operating on SHACL
(e.g., Java SHACL validators) use UTF-16
to represent the text and do not support
some parts of the Python regex dialect.
For example, in the input meta-model
specification, we omit the minimum bound 0
(e.g., {,4}), which breaks with the Java
regex engine beneath the SHACL validator.

Instead, with this patch, we parse the pattern
from the specification and re-render it into the
form that we also use in JSON Schema. We pick
JSON Schema regex dialect as most
SHACL validators in the wild can deal with it,
in particular those based on Java as a platform.
Hence, we decide to serve this
user base with priority.

Discovered in aas-core-meta issue 342.
Fixed in aas-core-codegen commit e22cc.

XSD

Adapt XML Schema for some schema validators

Previously we did not define aas:environment
directly via an xs:element tag, rather only
provided it directly as xs:complexType.
This created issues with several XML Schema
validator engines.

Fix #457.