[Java.Interop.Tools.JavaSource] Improve <a> parsing

[pjcollins]

Parsing for <a/> elements has been improved to fix all 83 cases where
conversion to a <see/> element would fail. Some examples of such
failures include:

## Unable to parse HTML element: <see href=https://www.sqlite.org/pragma.html#pragma_journal_mode>here</see>
System.Xml.XmlException: 'https' is an unexpected token. The expected token is '"' or '''. Line 1, position 11.

## Unable to parse HTML element: <see href="https://github.com/google/libphonenumber>libphonenumber</see>
System.Xml.XmlException: '<', hexadecimal value 0x3C, is an invalid attribute character. Line 1, position 67.

## Unable to parse HTML element: <see href="https://material.io/guidelines/components/progress-activity.html#progress-activity-types-of-indicators">
Progress & activity</see>
System.Xml.XmlException: An error occurred while parsing EntityName. Line 2, position 11.

## Unable to parse HTML element: <see href=#BROKEN> broken</see>
System.Xml.XmlException: '#' is an unexpected token. The expected token is '"' or '''. Line 1, position 11.

## Unable to parse HTML element: <see href=http://www.ietf.org/rfc/rfc2045.txt>RFC 2045</see>
System.Xml.XmlException: 'http' is an unexpected token. The expected token is '"' or '''. Line 1, position 11.

When we encounter an <a/> element that points to code or a local path
we will now only include the element value in the javadoc, and not the
full href attribute value.

[jonpryor]

Parsing of `<a/>` elements would occasionally fail when they didn't
match our expectations/requirements:

  * Unquoted URLs, a'la `android/database/sqlite/SQLiteDatabase.java`:

        * <p> See <a href=https://www.sqlite.org/pragma.html#pragma_journal_mode>here</a> for more

    Resulting in:

        System.Xml.XmlException: 'https' is an unexpected token. The expected token is '"' or '''. Line 1, position 11.

    or a'la `java/io/PipedOutputStream.java`

        * @exception IOException if the pipe is <a href=#BROKEN> broken</a>,

    resulting in:

        System.Xml.XmlException: '#' is an unexpected token. The expected token is '"' or '''. Line 1, position 11.


  * Improperly quoted attributes, a'la `android/telephony/PhoneNumberUtils.java`:

        * Matching is based on <a href="https://github.com/google/libphonenumber>libphonenumber</a>.

    Resulting in:

        System.Xml.XmlException: '<', hexadecimal value 0x3C, is an invalid attribute character. Line 1, position 67.

  * Use of "raw" `&`, a'la `android/widget/ProgressBar.java`:

        * <a href="https://material.io/guidelines/components/progress-activity.html#progress-activity-types-of-indicators">
        * Progress & activity</a>.

    Resulting in:

        System.Xml.XmlException: An error occurred while parsing EntityName. Line 2, position 11.


Fix this by updating updating the `InlineHyperLinkOpenTerm` terminal
to *not* require `href`, and updating the `InlineHyperLinkDeclaration`
rule to better deal with whatever chaos is there.

When we encounter an `<a/>` element that points to code or a local
path we will now only include the element value in the javadoc, and
not the full `href` attribute value.

Replace the `IgnorableDeclaration` rule with an
`IgnorableCharTerminal` terminal.  TODO: why?  What's this *do*?

[pjcollins]

Replace the IgnorableDeclaration rule with an
IgnorableCharTerminal terminal. TODO: why? What's this do?

I was trying to lean on what was done in UnknownHtmlElementStartTerminal to "skip over" reserved characters with a low priority rule. The Irony docs are sparse and I didn't see a way to do this without extending Terminal.

This change fixed parsing for the <a href="mailto:nobody@google.com">nobody</a> cases, which were otherwise failing with:

 ParserMessages:
  Error (1:23): Syntax error, expected: #PCDATA, <tt>, <TT>, <i>, <I>, <a attr=, <code>, <CODE>, {@code, {@docRoot}, {@inheritDoc}, {@link, {@linkplain, {@literal, {@see, {@value}, {@value, @ , {, }, {@param, UnknownHtmlElementStart, </a>, </A>, </tt>, </TT>, </i>, </I>, </code>, </CODE>
<a href="mailto:nobody@google.com">nobody</a>
                        ^
ParserTrace:
  input=`<a href= (<a attr=)`; error? False; message=Shift to S2
  input=`"mailto:nobody (#PCDATA)`; error? False; message=Shift to S8
  input=``; error? False; message=Reduce on '<html inline decl> -> #PCDATA '
  input=`<html inline decl>`; error? False; message=Popped state from stack, pushing <html inline decl>
  input=``; error? False; message=Reduce on 'InlineDeclaration -> <html inline decl> '
  input=`InlineDeclaration`; error? False; message=Popped state from stack, pushing InlineDeclaration
  input=``; error? False; message=Reduce on 'InlineDeclaration+ -> InlineDeclaration '
  input=`InlineDeclaration+`; error? False; message=Popped state from stack, pushing InlineDeclaration+
  input=`@google.com">nobody</a> (InlineValue)`; error? True; message=Syntax error, expected: #PCDATA, <tt>, <TT>, <i>, <I>, <a attr=, <code>, <CODE>, {@code, {@docRoot}, {@inheritDoc}, {@link, {@linkplain, {@literal, {@see, {@value}, {@value, @ , {, }, {@param, UnknownHtmlElementStart, </a>, </A>, </tt>, </TT>, </i>, </I>, </code>, </CODE>
  input=`@google.com">nobody</a> (InlineValue)`; error? False; message=RECOVERING: popping stack, looking for state with error shift
  input=`@google.com">nobody</a> (InlineValue)`; error? False; message=FAILED TO RECOVER