shader: bundle vrend_glsl_strbufs

Refactor vrend_shader.c by packing glsl_main, glsl_hdr, glsl_ver_ext,
and indent_level into struct vrend_glsl_strbufs. Makes the parameter
lists of many functions more informative (as opposed to taking
only dump_ctx).

Signed-off-by: Ryan Neph <ryanneph@google.com>
Reviewed-by: Gert Wollny <gert.wollny@collabora.com>

src/vrend_strbuf.h

@@ -175,7 +175,7 @@ static inline bool strarray_alloc(struct vrend_strarray *sa, int init_alloc)
    return true;
 }
 
-static inline bool strarray_addstrbuf(struct vrend_strarray *sa, struct vrend_strbuf *sb)
+static inline bool strarray_addstrbuf(struct vrend_strarray *sa, const struct vrend_strbuf *sb)
 {
    assert(sa->num_strings < sa->num_alloced_strings);
    if (sa->num_strings >= sa->num_alloced_strings)