Adjust to new PHP annotation syntax

[thekid]

Use #[...] instead of << >>, see https://wiki.php.net/rfc/shorter_attribute_syntax

• [x] Support both in the first step in a patch level release
• [x] Add an E_DEPRECATED warning to << >> syntax in order to make unittests fail but production code work in next minor release
• [x] Remove support for << >> in next major release

[thekid]

Initial syntactic support added to xp-framework/ast https://github.com/xp-framework/ast/pull/7 though still missing inline attributes and support for multiple arguments

[thekid]

The pull request xp-framework/ast#7 can now be merged; and the dependency updated accordingly.

[thekid]

1️⃣ First step released in https://github.com/xp-framework/compiler/releases/tag/v5.2.0

[thekid]

2️⃣ With named arguments support in https://github.com/xp-framework/compiler/releases/tag/v5.3.0, we can now support rewriting annotations to more idiomatic PHP

[thekid]

3️⃣ With xp-framework/ast#9 merged, deprecation notices will be emitted (but production code continues to work!)

[thekid]

4️⃣ Released officially along with https://github.com/xp-framework/compiler/releases/tag/v5.4.0