[Ada] Handling of generalized indexing in ASIS

[Arnaud Charlet <charlet at adacore dot com>]

This patch introduces a new semantic attribute Generalized_Indexing, for
indexed_components that are instances of Ada 2012 container indexing operations.
Analysis and resolution of such nodes is performed on the attribute, and the
original source is preserved for ASIS operations. If expansion is enabled, the
indexed component is replaced by the value of this attribute, which is in a
call to an Indexing aspect, in most case wrapped in a dereference operation.
Otherwise the original node is type-annotated, which makes ASIS queries and
pretty-printing simpler.

Tested on x86_64-pc-linux-gnu, committed on trunk

2014-02-24  Ed Schonberg  <schonberg@adacore.com>

	* sinfo.ads, sinfo.adb: New attribute Generalized_Indexing, for
	indexed_components that are instances of Ada 2012 container
	indexing operations. Analysis and resolution of such nodes
	is performed on the attribute, and the original source is
	preserved for ASIS operations. If expansion is enabled, the
	indexed component is replaced by the value of this attribute,
	which is in a call to an Indexing aspect, in most case wrapped
	in a dereference operation.
	* sem_ch4.adb (Analyze_Indexed_Component): Create
	Generalized_Indexing attribute when appropriate.
	(Analyze_Call): If prefix is not overloadable and has an indexing
	aspect, transform into an indexed component so it can be analyzed
	as a potential container indexing.
	(Analyze_Expression): If node is an indexed component with a
	Generalized_ Indexing, do not re-analyze.
	* sem_res.adb (Resolve_Generalized_Indexing): Complete resolution
	of an indexed_component that has been transformed into a container
	indexing operation.
	(Resolve_Indexed_Component): Call the above when required.
	(Resolve): Do not insert an explicit dereference operation on
	an indexed_component whose type has an implicit dereference:
	the operation is inserted when resolving the related
	Generalized_Indexing.

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