RFR: 6725: Formalize agent probe definition XML schema and enforce validations

[Kangcheng Xu]

This pr implements [JMC-6725: Formalize agent probe definition XML schema and enforce
validations](https://bugs.openjdk.java.net/browse/JMC-6725). XMLs supplied by users are validated against
[`jfrprobes_schema.xsd`](https://github.com/tabjy/jmc/blob/a4da862b744f407f3262f006e302515c142e9482/agent/src/main/resources/org/openjdk/jmc/agent/impl/jfrprobes_schema.xsd)
on registry creation and modification.

Notable changes in configuration probes format are:
- `<parameter>` elements now should be enclosed by a `<parameters>` element, and
- `<field>` elements now should be enclosed by a `<fields>` element

Type checking is enforced on most elements. Additionally, the following types are restricted with regular expressions
checking elements' text node contents:
- `classType` for `<class>` and `<converter>` elements
- `methodNameType` for `<name>` elements
- `descriptorType` for `<descriptor>` elements
-  `pathType` for `<path>` elements, and
- `expressionType` for `<expression>` elements

Please test, especially on regex, as I'm not entirely confident they cover every cases and don't yield false negatives.

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Commit messages:
 - Update license header year numbers
 - Fix test, remove <thread> and <kind> elements
 - Define xsd schema, implement and enforce validations

Changes: https://git.openjdk.java.net/jmc/pull/66/files
 Webrev: https://webrevs.openjdk.java.net/jmc/66/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JMC-6725
  Stats: 618 lines in 6 files changed: 400 ins; 36 del; 182 mod
  Patch: https://git.openjdk.java.net/jmc/pull/66.diff
  Fetch: git fetch https://git.openjdk.java.net/jmc pull/66/head:pull/66

PR: https://git.openjdk.java.net/jmc/pull/66